The Scientific
Method, Bias, and
Reasoning
2
Truth is sought for its own sake. And those who are engaged upon the quest for anything for
its own sake are not interested in other things. Finding the truth is difficult, and the road to
it is rough.*
2.1 Introduction
The hallmark of any successful crime scene investigation is a team effort whose director,
like the maestro of an orchestra, is its leader. How well the team performs is related to how
well its leader uses the scientific method, thinks critically and creatively, opens lines of
communication with subordinates, and applies inductive, deductive, and abductive logic.
If done properly the culture of science wraps its arms around the team and protects it from
making critical mistakes, introducing subjectivity, and conducting a biased investigation.
This is true because science itself is self-correcting. Mistakes, when found, are corrected,
and biases, through team effort and the application of the scientific method, are avoided.
As Chisum and Turvey wrote [2],
Evidence interpretation is a complex process, and the less one understands about the nature
of physical evidence, the principles of forensic science, analytical logic, and the scientific
method, the simpler crime reconstruction may seem. (p. 92)
When asked how the crime was solved or the most probative evidence located, no
crime scene investigator would consciously say,




―I used the scientific method to solve this crime,‖ or
―The scientific method pin-pointed the most important evidence at that scene,‖ or
―My creative employment of induction and deduction led me to the killer,‖ or
―I ensured that I had an open line of communication with my subordinates.‖
That is not how science and scene investigation work. Most if not all crime scene investigators never consciously consider their cognitive thoughts, that is, the reasoning process
they employ after or during the investigation. It becomes and should be second nature.
Their approach is based on education, intuition, training, and experience. The scene scientist’s approach is different, however, because it is based on deductive and inductive reasoning buttressed by education, intuition, training, and experience.
Chapter 1 suggested that crime scene investigation is not simply the application of science but actually a complex scientific endeavor. As such, it is, like all science, a step-wise
* Stated by Alhazen (Ibn Al-Haytham) in his Critique of Ptolemy, translated by S. Pines, Actes X Congrès
internationale d’histoire des sciences, Vol. I. Ithaca, 1962, as quoted in Ref. [1].
32
Crime Scene Forensics
process of knowledge and information-building about understanding what happened, who
might have done it, and what probative evidence is available. It is also a problem-solving
exercise. For example, why did this happen and in what sequence? Obtaining as precise an
answer as possible illustrates why crime scene investigation is particularly suited to the
application of the scientific method. If we delve further into the reasons, the explanation of
why this is true is plainly clear. Just as scientists attempt to explain observations through a
series of constantly tested and revised hypotheses, the ultimate feedback mechanism, using
what is called the scientific method, so do scene scientists.
2.2 The Scientific Method: Scene Scientists and Scene Investigators
Authors of science text books nearly invariably include a discussion of the scientific method,
by typically listing the so-called steps inherent in the method, often offering an appropriate
diagram spiced with an example or two. Over the years, there have been scholarly articles
on the subject. As Cohen says [3],
According to the currently fashionable view, it is of the very essence of the scientific method to
distrust all reason to rely on the facts only. The motto, ―Don’t think; find out,‖ often embodies this attitude. The scientific method is supposed to begin by banishing all preconceptions
or anticipations of nature. In the first positive stage it simply collects facts; in the second,
it classifies them; then it lets the facts themselves suggest a working hypothesis to explain
them. It is only in the last stage, in the testing or verifying of hypotheses (so as to transform
them into established laws) that the rational deduction of consequences plays any part. Such
deduction, it is maintained, brings us no new information. It only makes explicit what experience has already put into our premises.
Most scientific texts list five to seven steps inherent in the scientific method. Edmund
lists eleven on his Web site [4]. While his is one person’s opinion, students of science will
recognize the following widely accepted list, which tracks Cohen’s explanation quoted
above.





Observe a phenomenon that has no good explanation (potential evidence,
which we label as observable phenomena)
Formulate a hypothesis
Design an experiment(s) to test the hypothesis
Perform the experiment(s)
Accept, reject, or modify the hypothesis
By itself, this list offers little insight to its application to a specific scene investigation.
To illustrate, consider an example of a homicide scene examined applying the scientific
method. The following are the gross observations—the macro scene (see Chapter 4). The
micro scene is not considered in this discussion.

A deceased male is lying face up on the floor in his bedroom, the victim of a
single stab wound to the chest.

He has an incised wound (a deep cut) on his right forefinger.

His shirt, which is torn, has drip pattern in blood on the chest.

The front door is open.
33
Crime Scene Forensics
 The living room window is open.

A sneaker print in dust is on the floor under the window.

Dried droplets—not blood—mar some of the sneaker print detail.

A dry but diluted drop of blood is in the kitchen sink.

A crumpled paper towel with dried blood sits on the kitchen sink.

A shattered drinking glass is on the kitchen floor near the sink.

A wicked storm with high winds passed through the town several hours earlier.
All scenes have multiple gross observable phenomena (macro-scene elements), much
of which has no immediate, simple, reasonable, or seemingly logical explanation. Additionally, each might have many explanations of which only one rests in the ground truth.
Frustratingly, most explanations will never be known with absolute certainty because,
other than the participants of the crime, investigators were not present when the event took
place. Thus, the essence of all scene investigations is sorting fact from fiction, identifying
what is crime-related and eliminating what is not.
One can generalize the observable phenomena and place them into arguable categories.
It would be instructive for novice investigators and students to place these observations
into usable categories such as:




People living their lives
Activity of the crime that spawned the investigation
Activity or events unrelated to neither of the above
Unknown at this time
All observable scene phenomena must be interpreted correctly, that is, put into a category correctly, or risk being misinterpreted. If misinterpreted, the result can be a botched
investigation leading to the arrest and conviction of an innocent person. Scene investigators use their experience and intuition to understand these macro-scene elements. Certainly,
using experience to interpret new phenomena is a normal extension of an engaged mind,
and it is reasonable. It is, however, the seed of experienced-based bias, which is the natural
consequence of living and working in the real world. Bias happens subconsciously and,
while not necessarily bad if controlled, it can lead the scene scientist/investigator down an
incorrect interpretive path. Called the ―I’ve seen it a million times‖ syndrome, everyone
pigeonholes their experiences and past scene observable elements they use to interpret
scene elements in each new setting. The result is a mixture of correct and incorrect interpretations of what the scene is trying to tell them.
What differentiates scene investigators from scene scientists is how they use their experience and intuition to arrive at final interpretations or conclusions. Scene investigators
trust their experience and draw final conclusions based on their observations over time.
This seems reasonable but, in truth, is a myopic approach because the process automatically arrests the mental exercise once they have ―decided‖ what happened. The scene scientist, however, never offers a ―final‖ interpretation or conclusion until all hypotheses have
been ―tested‖ and alternative explanations exhausted. The word ―final‖ is in quotes because
even the final conclusion offered can change if new evidence is located. It is this ―testing‖
of alternate explanations that separates scene investigators from scene scientists. Table 2.1
illustrates the first thought processes leading to hypotheses based on observable phenomena at the scene.
34
Crime Scene Forensics
Table 2.1 First Hypotheses Based on Scene Observations
Gross Observable Phenomena
Deceased on floor with single stab wound to chest
Deep incised wound to right forefinger
Drip pattern of dried blood on the shirt of the
deceased
Initial Interpretation (Hypothesis)
Deceased stabbed by assailant and died quickly
Defensive wound—deceased knew what was
happening and was fighting for his life
Result of stab wound or blood dripping from knife
Storm passed through hours earlier
Living room window is open
No immediate causal relationship to crime
Perpetrator entered the house through window
Dry residue sneaker print on floor under window
Dried droplets mar sneaker pattern
Front door open
Dried, diluted drop of blood in kitchen sink
Perpetrator’s sneaker print
Window was open before storm
Perpetrator’s exit route
Perpetrator was injured and went to sink to wash
after committing crime
Perpetrator used towel to clean and dry wound
Altercation began in the kitchen with perpetrator
struggling with deceased here
Paper towel with dried blood on kitchen sink
Shattered drinking glass on kitchen floor
These explanations of observable phenomena seem reasonable and they may be all the
explanation needed. However, a scene scientist considers these as testable hypotheses, each
having an alternative explanation. Thus, this is the first round of observational explanations, some of which might be correct and others incorrect. If this is as far as an investigator goes, which is essentially jumping to conclusions without considering reasonable
alternatives, the scene is open to missing important probative evidence.
The next step requires the formulation of alternative hypotheses, which is the essence
of the scientific method. Returning to the homicide scenario, the scene scientist formulates
alternative scenarios. The result is shown in Table 2.2, an expansion of Table 2.1. Here, the
third column offers alternative explanations of the macro-scene observation scenarios, different from those in the first column and also perhaps more reasonable.
These alternative explanations also have merit but, regardless, the ground truth remains
unknown. In fact, it might lie somewhere between the two hypotheses. Or, a third as yet
unconsidered alternative might be closer to what actually happened. At this point, these
are competing hypotheses. New evidence could trigger a third set of hypotheses or eliminate one of the original two. The point is that the best fact-fit can be only determined
through experimentation, step 3 of the scientific method. For students and novice investigators, the concept of experimentation is often frightening because it forces them into
unknown intellectual territory. Experimentation, however, does not necessarily require or
necessarily imply actual laboratory experiments, although that is certainly a possibility.
From a crime scene perspective, some experimentation can be done at the scene, which
might result in a change of one of the hypotheses or even create new ones. Laboratory testing might be done on evidence collected and transported to the forensic laboratory. If laboratory experimentation is necessary, the best interpretation of what happened and the
sequence of events would be put on hold.
Table 2.3 proposes possible experiments (see the last column), not all of which are
laboratory-based. The idea is not to design a way to prove the original or alternative
hypotheses but to disprove them. In fact, the scientific method requires that the experiment’s intended design is to disprove projected hypotheses. This not-so-subtle fact is lost
The Scientific Method, Bias, and Reasoning
35
Table 2.2 Alternative Scenarios Based on Observable Phenomena at the Scene
Gross Observable Phenomena
Initial Hypothesis
Alternative Hypothesis
Deceased on floor with single stab
wound to chest
Deep incised wound to right
forefinger
Deceased stabbed by assailant
and died quickly
Defensive wound—deceased
knew what was happening and
was fighting for his life
Deceased fell on knife and died
quickly
Deceased cut finger picking up
shards of glass from floor
Drip pattern of dried blood on the
shirt of the deceased
Result of stab wound or blood
dripping from knife
No immediate causal relationship
to crime
Result of blood dripping from cut
finger
Perpetrator entered the house
through window
Deceased opened window to
cool house before crime
took place
Perpetrator’s sneaker print
Victim’s sneaker print
Dried droplets mar sneaker
pattern
Window was open before storm
Window was open before storm.
Droplets might have happened
during storm if storm blew open
window
Front door open
Dried, diluted drop of blood in
kitchen sink
Perpetrator’s exit route
Perpetrator was injured and went
to sink to wash after
committing crime
Perpetrator used towel to clean
and dry wound
Altercation began in the kitchen
with perpetrator struggling with
deceased here
Blown open by storm
Deceased tried to clean wound
after cutting finger on glass
shards
Deceased tried to stop bleeding
with paper towel
Deceased dropped glass when
storm blew open front door
Storm passed through hours
earlier
Living room window is open
Dry residue sneaker print on floor
under window
Paper towel with dried blood on
kitchen sink
Shattered drinking glass on
kitchen floor
Storm blew open front door
on most lay investigators [3]. It is also expected that these experiments might create new
hypotheses, which triggers more testing.
A time will come when all data have been analyzed, hypotheses tested and retested,
and a point will be reached when no more testing seems reasonable or warranted. Then, a
truth of some sort will emerge. This truth may not represent the actual ground truth, but
will be closer than if the process had been stopped after the first set of hypotheses. The
process may have led to new evidence that should have elicited additional questions and
perhaps new hypotheses.
In the example above, what would the investigative result have been if the investigator
solely relied on the initial interpretation of the events? Possibly, the evidence collected and
subsequently analyzed by a forensic laboratory would have represented that investigator’s
experience-based bias, which would be myopic in scope. By considering all alternative
scenarios, the scene scientist/investigator permits the self-correcting mechanism inherent
in the scientific method to dictate the flow of the investigation and the evidence discovery
process.
This is why the scientific method, applied correctly, is the only way to eliminate bias in
an arena where there are few, if any, checks and balances. By its very nature, the scientific
method conducts those checks and balances through the hypothesis, experimentation, and
feedback process. For science students, this process makes sense. For novice and many
36
Crime Scene Forensics
Table 2.3 Proposed Experiments to Disprove Advanced Hypotheses
Gross Observable
Phenomena
Initial Hypothesis
Deceased stabbed by
assailant and died
quickly
Alternative Hypothesis
Deceased fell on knife
and died quickly
Deep incised wound to
right forefinger
Defensive wound—
deceased knew what
was happening
Deceased cut finger
picking up shards of
glass from floor
Drip pattern of dried
blood on the shirt of the
deceased
Result of stab wound
or blood dripping
from knife
Result of blood
dripping from cut
finger
Storm passed through
hours earlier
Living room window is
open
No immediate causal
relationship to crime
Perpetrator entered
the house through
window
Storm blew open front
door
Deceased opened
window to cool house
before crime took
place
Dry residue sneaker print
on floor under window
Perpetrator’s sneaker
print
Victim’s sneaker print
Dried droplets mar
sneaker pattern
Window was open
before storm
Window was open
before storm. Droplets
might have happened
during storm if storm
blew open window
Deceased on floor with
single stab wound to
chest
Front door open
Perpetrator’s exit route Blown open by storm
Possible Experiments
 Examine report of the
medical examiner
 Look for other signs of
struggle
 Check fingerprints
 Examine medical
examiner’s report
 Look for shards of
glass with blood
 DNA analysis of blood
 Examine bloodstain
pattern expert’s
interpretation of drip
pattern
 DNA testing on blood
See entry ―Front door
open‖ below
 Check for pry marks
 Check finger marks
not matching
deceased
 Check victim/other
footprints on ground
Check sneaker of victim
Check storm wind
direction
• Check storm wind
direction
• Check jimmied or
Dried, diluted drop of
blood in kitchen sink
Perpetrator was
injured and went to
sink to wash after
committing crime
Deceased tried to clean
wound after cutting
finger on glass shards
Paper towel with dried
blood on kitchen sink
Perpetrator used towel
to clean and dry
wound
Altercation began in
the kitchen with
perpetrator struggling
with deceased here
Deceased tried to stop
bleeding with paper
towel
Deceased dropped glass
when storm blew open
front door
Shattered drinking glass
on kitchen floor
broken locks
 Check impact area
where door should
have hit wall
DNA analysis of blood
 Bloodstain pattern
 DNA of blood
 Check glass for blood
 Check for crushed
shards on shoe of
deceased
The Scientific Method, Bias, and Reasoning
41
experienced investigators, this is a foreign concept. For scene investigators as opposed to
scene scientists, the approach is not necessarily satisfying because it offers only a sketchy
roadmap of how to conduct a competent scene investigation. This is the reality of the scientific method. Scientific processes are complex. Scene investigations, too, are complex
and without question a scientific endeavor. Using a cut-and-dried method for conducting
a scene investigation is ludicrous.
The above homicide example was intentionally simplistic because it was intended to
illustrate the scientific thought process. In the current paradigm of crime scene investigation (Chapter 1), police investigators apply scientific methods at crime scenes without using
the scientific thought process. Like researchers, scene scientists create new understanding
because they use what is known to uncover the truth of the unknown, that is, the truth
underlying alleged facts. Unlike scene scientists, researchers question the unknown and
use the scientific method to uncover more basic truths. Despite these disparate missions,
scene scientists and basic researchers use a common approach to accomplish their goals.
The foregoing discussion makes it seem as though scene scientists and scene investigators exist on different planets. Nothing could be further from the truth. The discussion
is not meant to imply that scene scientists and police investigators do not and cannot play
on the same field, even if their individual roles and missions are decidedly different. In
fact, they are complementary. At the crime scene, the scene scientist conducts the business
of science distinct from but complimentary to the investigative role of the police scene
investigator. The scientific mind places a premium on precision, objectivity, repeatability,
experimentation, uncertainty management, peer review, and experience in order to arrive
at reliable interpretations of clues left at the scene because these methods have a history of
successfully relating information while correcting misunderstandings.
The scene scientists’ approach is radically different from that of the scene investigator,
whose mission is to find and arrest the perpetrator. The scene scientist has no mission or
allegiance except to the facts. The scene investigator searches for facts (evidence) to fit a
scenario or an ―idea‖ of what happened based on experience or on information relayed by
messengers—witnesses, other officers, and so on, as the cartoon above implies. Still, they
play on the same team. One is the pitcher and the other the catcher. Is the scene scientist
the pitcher or the catcher? The reader should decide.
2.3 Bias in Scene Investigations
Scene scientists judge facts, understanding that one must define facts carefully; some facts
are hard and others are soft. The competent scene scientist remains loyal to the hard facts,
such as scientific data, observable phenomena, and so on, and seriously considers only
undeniably supportable soft facts, such as witness statements, and so on. Each new fact
must pass muster by testing against an appropriate hypothesis. Only when all of the facts
are known can a scenario of what happened be reliably expressed. New facts that do not
fit must have an explanation, which means a new or modified hypothesis. Without this
process, investigations are prone to bias. According to Dror, an expert studying human
behavior, and Rosenthal [5]
Human judgments are affected by a variety of factors. These effects stem from our initial
perceptual mechanisms to higher cognitive functions. Given such variability and individual
differences, the question arises: How reliable are human judgments? The variability across
38
Crime Scene Forensics
individuals reflects that people are different; they have different past experiences, mental
representations and abilities, as well as different motivations, personalities, and so forth.
(p. 900)
Scene investigators will likely bristle at the suggestion that they are biased in their
work. They correctly believe crime scene investigation is a critical process and, as such,
they strive to find evidence to support a successful prosecution. They would likewise challenge the suggestion that they do not actively search for exculpatory evidence because their
subconscious minds are focused on prosecutions. This should not come as a surprise. Scene
investigators in the United States mostly represent the investigative arm of law enforcement and, thus, are an integral part of the prosecution team. Their mission is to find probative evidence to prove someone committed the crime, which they do through a process of
deductive reasoning, where, if their premises are true, the conclusion must also be true. By
definition, then, they are as biased as the crime scene expert hired by the defense team.
The prosecutor, who is an integral player and arguably the most critical member of the
prosecution’s adversarial team, is by definition also biased. But the prosecutor, as an advocate, is supposed to be biased; so is the defense attorney. The scene scientist who responds
to the scene and who is likely employed by the prosecution’s team must resist the inherent
biases and should have no stake in the investigative process. The reason is that science
brings objectivity to the investigative process. That is not to imply that a scene scientist
cannot be swayed by reason.
Science researchers use the scientific method to eliminate bias. If the researcher conducts experiments to arrive at a preconceived result, the process is not science. Researchers
work at a frontier of the unknown, an area of uncertainty, where the work is a continual
process of discovery propelled by the scientific method as the guiding principle. The scientific community conducts research and presents and/or publishes the work in scientifically
acceptable venues. There, the review process takes place and sanctions occur, albeit usually
at a later time. The researcher is, in essence, saying, ―Look what I’ve done. Take your
best shot.‖ This is the process by which science tests itself and reveals errors before they are
widely disseminated. In this way, too, science finds scientific fraud and thus is selfcorrecting through the process of peer review, publication, and collegial interactions (e.g.,
sharing at conferences). Unlike law enforcement, the culture of science encourages and
rewards critical questioning of past results and its colleagues. The scientific culture encourages cautious, precise statements and frowns on statements that venture beyond facts; it is
acceptable for colleagues to challenge one another, even if the challenger is junior. This is
not what happens in the scene investigative arena.
The issue is that each scene investigation should be thought of much like a research
project. At crime scenes, scene scientists/investigators are working at the frontier of the
unknown, of uncertainty. But unlike scientific research, there is no fall-back position and
rarely peer review. In fact, most criminal cases have no contemporary review process, no
peer review, and thus no mechanism to uncover shoddy, biased, or fraudulent work. The
scientific process is the antithesis of what happens in real-life crime scene investigations.
Unfortunately, the following are real-life events:




Planting evidence at a crime scene to point to a defendant.
Collecting evidence without a warrant by claiming exigent circumstances.
Ignoring evidence at a scene that might exonerate a suspect.
Failing to report a colleague, superior, or subordinate for inappropriate activity.
The Scientific Method, Bias, and Reasoning
41
Many types of bias exist to which investigators and scientists are prone. Examples are
shown in Table 2.4. Forensic examples were added to illustrate relevance.
With respect to bias in the forensic sciences, which is equally true for crime scene
investigation, Risinger and Saks [6] wrote,
When everyone from Nobel prize winners to average citizens . . . take steps to make sure their
judgments are not distorted by extraneous context information, then it is hard to conceive of
what it is that makes forensic scientists think they are immune from the same effects. (p. 51)
Of particular relevance is that these ideas with respect to crime scene investigation are
not new. May wrote in 1936 [7], and Cooley and Turvey [8] reported later,
. . . often the most significant bit of evidence is overlooked or misinterpreted because someone
has jumped to a premature conclusion.... To face a crime with an open mind—a mind willing to believe and disbelieve even its own senses, sometimes willing to admit and desert one
lie of investigation for another, is one of the most difficult tasks of the detective. (p. 71)
Uncertainty is the breeding ground for bias and two factors are at work: ambiguity and
subjectivity. In the former, if the evidence or the circumstances are incomplete, murky, or
equivocal, the scene scientist—or the crime scene investigator—is free to develop opinions,
which can represent the analyst’s personal bias, for example, slanting interpretations
toward the prosecution’s view of a case or searching for scene evidence based on an arrest
or a colleague’s description of the assailant. When subjectivity is the issue, scene interpretations rest on an examiner’s experience or beliefs which results in bias. Prejudices and
biases occur during decision-making situations where the decisions represent a gray area,
typically where there is ambiguity and subjectivity [8,9]. In black-and-white situations,
decisions are typically straightforward and easy: Where do we cordon off the broadcast
and print media during the investigation? Who on the team is the spokesperson for the
media? Where is the command center? When should we look for fingerprints? Such groundball questions have definite answers.
Table 2.4 Forensically Important Categories of Bias
Bias Name
Bandwagon effect (also
groupthink, herd
behavior, manias)
Bias Description
Forensic Example
Tendency to do or believe things
because many other people do
The prosecutor or detectives are certain a
suspect is the killer because he is a ―bad
guy.‖ At the scene, this knowledge could
sway the course of the investigation
especially if the scene investigators know
who the ―bad guy‖ is.
Confirmation effects
The tendency to search for or
interpret information in a way
that confirms one’s
preconceptions
The crime scene investigator who has a
preconceived idea of what happened or
who committed the crime and searches the
scene to uncover evidence to support that
notion.
Observer-expectancy
effect (also observer
effects, context effects,
expectancy effects)
The expectation of a given result
with the unconscious
manipulation of an experiment
or misinterpretation of data in
order to find it
An analyst expects a result but does not get
it, and then creates scenarios so that the
correct results are not obtained. The crime
scene investigator ignores evidence that
does not fit a specific theory of the case.
40
Crime Scene Forensics
Some decisions are not straightforward, however: What does the bloodstain spatter
pattern on a wall mean? What technique will best visualize latent prints on a door knob—
super glue fuming or dusting with powders? How should we enhance a wet residue footwear impression? Can we lift it? Is it really a wet residue print? How do we know? Which
enhancement chemicals should we use? Should we do it at the scene or should we try to
collect it? What is the bullet path through the car? Where was the shooter standing?
No one corners the market on making bad decisions, certainly not scene scientists,
forensic scientists, or crime scene investigators. Everyone has biases and everyone makes
decisions based upon them. But bias does not belong at crime scenes or in the forensic laboratory. Thus, it must be controlled. The first example comes not from a crime scene investigation but from what has been termed the ―Gold Standard‖ [10] of forensic science—DNA.
2.3.1 Case Example 1
An example of ambiguity involved a decision made with respect to the reporting of DNA
statistics. The deceased was found naked on his bedroom floor. The crime scene unit (laboratory scientists) found a hair on the body of the deceased, and the laboratory’s microscopic analysis reported that the hair was different from that of both the deceased and the
defendant. This must have been a blow to the prosecution because it meant that physical
evidence found at the scene did not belong to the person the prosecutor had on trial:
believed to be a lone killer. The ensuing DNA analysis was critical for the prosecution
because, had the DNA conclusively matched either the defendant or the victim, the microscopic analysis would not have mattered.
The first analytical decision the laboratory made after the microscopic examination was
incorrect. At that time, and at the time of writing this text, the first line of DNA attack after
microscopic analysis of hair was to perform mitochondrial DNA typing. Instead, the laboratory chose to analyze for nuclear DNA, the results of which were not a typical DNA match;
according to the laboratory, the DNA results matched the victim but the statistics were not
stellar: 1 in 493 or almost 1 in 500. Still, the statistics clearly favored the prosecution’s view
of the case. A closer look at the statistics showed that the laboratory tailored the statistics to
favor the prosecution, whether intentionally or not. Had the DNA calculations been made
in an unbiased way, the statistics would have been 1 in 6, a huge difference in determining
whose hair it was or was not [11]. The second example is a crime scene example [12].
2.3.2 Case Example 2
The brutal murder of a 20-year-old woman, presumably by her ex-boyfriend is an example
of extreme on-scene bias and incompetence. The prosecutions alleged factual history
follows:

Ex-boyfriend breaks down glass door to the house to come after his exgirlfriend, who is dating someone else.

He grabs a chef’s knife from a knife holder in the kitchen and chases his exgirlfriend to an upstairs bathroom.

He butchers the ex-girlfriend, slashing her head and throat with the knife.

He stabs himself in the chest and leaves the bathroom, goes down the stairs
and falls at the foot of the stairs next to the kitchen where he remains until found by
the police.
The Scientific Method, Bias, and Reasoning
41
 The ex-girlfriend’s sister calls her father who calls the police.

The father is first on the scene. He finds his daughter and then the exboyfriend. He begins kicking the ex-boyfriend in the head.
 One of the officers on the scene is the uncle of the deceased. He does not leave the
scene.

The father is still at the scene.

The on-scene investigation is incomplete, presumably because the police
conclude that the ex-boyfriend is the murderer.
 In addition to the above, the on-scene work was shoddy or simply not considered
important since the ―actor‖ was in custody.

They photographed evidence of the scene without scales and without using a
tripod. Most photographs were taken at an angle.
 Bloody footprints in the bathroom were not photographed properly nor were they
enhanced (see Figure 2.1).
 Bloody footprints in the hallway outside the bathroom and in the kitchen were
not enhanced. No on-scene comparisons were made of the class characteristics of
the bloodstained footwear impression prints to the shoes of the deceased, the exboyfriend, or the father.

No fingerprinting was performed at the scene.

The ex-boyfriend’s clothing and shoes were not examined at the scene or by
the crime laboratory for glass shards.

The bloodstain spatter patterns in the bathroom were not interpreted.

A bloody knife found in the bathroom was processed by the police latent print
laboratory using Amido black. Stained friction ridge detail is observed, but the
laboratory reports an inability to raise latent prints (see Figure 2.2).
 BPA of the staining on the knife does not support the contention that the exboyfriend stabbed himself after murdering the ex-girlfriend.
Figure 2.1 Bloodstained footprint at scene. (Photograph by Robert C Shaler)
42
Crime Scene Forensics
Figure 2.2 Amido black stained bloody knife handle. (Photograph by Robert C. Shalerj
So how can biases be eliminated or at least minimized at the crime scene? One way is
to change the existing crime scene paradigm (see Chapter 1). The reason is that science is
self-correcting because of the inherent challenges built into the scientific method and the
need for peer review. Such a process does not exist during or after a crime scene investigation. However, if each crime scene is considered a research project unto itself, the selfcorrecting process must be completed within a timeframe dictated by the case situation.
Certainly investigators can and do return to crime scenes, but unlike scientific research,
where additional experiments can be run, when the crime scene is released, it is finished.
How does one integrate the self-correcting aspect of science into the scene investigation
process? Science does it by challenging hypotheses developed by the scientific method and
by peer review. Challenging investigative hypotheses at a crime scene is difficult because
scene investigators are usually from the same agency, and attempting this may require challenging a supervisor. In a paramilitary organization such as the police, this can lead to
professional suicide. The ideal is a team leader who is willing and open to having intellectual
discussions concerning alternative hypotheses during the investigation. Hopefully, the discussion would be openly challenging. Theoretically, this ideal is certainly possible, and in
some jurisdictions it may well happen. How well it works will depend on the team leader
because the personality of each team is different, and each team leader has different relationships with subordinates.
The openness of such discussions depends on the ego, self-esteem, and self-assuredness of the team leader. If the team leader’s ego and/or decisions are not at least open for
discussion, his/her evolving emotions may get in the way of a competent investigation, as
the team leader’s opinions and ideas will become the final arbiter in how the investigation
proceeds. Figure 2.3 illustrates how a meaningful investigation can be severely compromised. The team leader is not open to suggestions that might call into question his authority or his ego. The dark arrows indicate closed or minimally open lines of communication.
In these situations, opposing hypotheses may not be seriously considered or might even be
considered a threat to the team leader’s authority, even though the purpose is to solve the
crime. This emotional blockage of information between the team leader and subordinates
is illustrated in Figure 2.3.
The Scientific Method, Bias, and Reasoning
45
Team leader
Hypotheses
Subordinate investigator
Figure 2.3 Truncated information flow between subordinates and team leader.
However, a scientist at the scene can change the dynamics of the team’s personality.
The scientific presence automatically brings a sense of objectivity that should not be challenged. Certainly there will be personality conflicts and differences in authority, but the
scientist should not be the team leader’s subordinate. In time, conflicts will be minimized
as scientists and investigators establish a healthy working relationship. Individual team
members might feel apprehensive about challenging their superior, but the scientist should
not, as the palm print example in Chapter 1 illustrated.
When the scientist enters the investigative arena, Figure 2.3 changes and should appear
more like Figure 2.4. The green arrows show open lines of communication. The yellow
arrows represent a partially open communication path. The dark arrows, as in Figure 2.3,
indicate minimal effective communication, such as the team leader instructing subordinates with respect to the scene investigative process.
The subordinate-to-team leader openness might still be truncated, but the scientist and
the team leader should have an open dialogue. In fact, the scientific presence can open lines
of communication such that an open forum can occur among all scene investigators: scientist, team leader, and subordinates. Certainly this is the ideal. It opens the possibility that
the scene will be processed as it should: as a research project amid uncertainty and chaos.
Figure 2.4 Lines of communication among team members.
Information flow
Criminalist
Criminalist
Hypotheses
Hypotheses
Team leader
Hypotheses
Subordinate
investigator
Team leader
Hypotheses
Subordinate
investigator
44
Crime Scene Forensics
The forgoing underscores the self-correcting, bias-mitigating capabilities of the scientific approach in crime scene investigations. Without a scientific presence at the scene, the
investigation is prone to bias, error, and subjectivity, none of which has a place in an environment in which ambiguity and uncertainty prevail. Since many if not most scene investigations have no contemporaneous peer review process, the scientific approach is the only
way to protect the integrity of the investigation.
2.4 Reasoning
There is little doubt that a form of reasoning takes place during any crime scene investigation. And since crime scene investigation is a scientific process and the direct application
of the scientific method, there must be logic and reasoning. Is it a deductive or an inductive
process? To explore these possibilities, definitions are in order.
Deductive reasoning works from the general to the more specific and is often referred
to as a ―top-down‖ process of logic. It begins with a theory and moves to a testable hypothesis. Testing or verification requires observations or experiments that address the hypothesis which is ultimately either confirmed or not. This feels like what happens at crime
scenes. Concerning deductive criminal profiling, Turvey says [13],
The advantages of the Deductive Criminal Profiling model are very important. This model
requires specialized education and training in forensic science, crime scene reconstruction,
and wound pattern analysis. . . . Deductive Criminal Profiles tend to be more specific than
Inductive Criminal Profiles, assisting greatly in the major goal of the profiling process, which
is to move from a universal set of suspect characteristics to a more unique set of suspect
characteristics.
Inductive reasoning begins with an observation and moves to a testable tentative
hypothesis, which is more open-ended. This also feels like what happens at crime scenes.
From there, a theory is derived, which must be confirmed. In short, it moves from the
specific to the general and is thought of as a ―bottom-up‖ process of logic or reasoning.
Inductive criminal profiling, Turvey [13] says, is:
The process of profiling criminal behavior, crime scenes, and victims from the known behaviors and emotions suggested by other criminals, crime scenes, and/or victims. In essence, as
the term suggests, this is reasoning from initial statistical data to specific criminal offender
behavior. In any event, Inductive Criminal Profiling is generally the result of some kind of
statistical analysis, or finds it’s reasoning in cases outside of the case at hand.
Both deductive and inductive reasoning are illustrated in Figure 2.5.
Crime scene investigations require both types of reasoning simultaneously. And by
examining the above closely, it certainly appears that an overlap exists. It might be possible
to assemble both into a singular concept that continuously cycles from theories to observations and back again to theories. In fact, researchers often observe patterns in data that lead
to the development of new theories—an inductive process.
All branches of natural science use inductive reasoning and establish theories and
laws of nature based on observation and on deductive reasoning to draw conclusions.
There are circumstances where observations come first. One might observe certain facts
that form a pattern that eventually leads to tentative hypotheses, which are tested to form
The Scientific Method, Bias, and Reasoning
45
Theory
Hypothesis
Observation
Confirmation
Theory
Tentative
hypothesis
Pattern
Observation
Figure 2.5 Illustration of deductive and inductive reasoning.
the basis of a theory. Still, the theory must be confirmed, which would be abduction.
Gudwin wrote [14],
We propose understanding abduction not as the process of anomaly detection (which would
be deduction), neither as the process that generates hypothesis (which would be induction)
but as the test selection of those hypotheses.
In this context, confirmation is a process that invokes another type of reasoning—
abductive reasoning. A combined process of inductive, deductive, and abductive reasoning
appropriate for crime scene investigation is illustrated in Figure 2.6.
From a practical perspective, does defining how reasoning fits the crime scene investigation help? Many believe the process is intuitive and subject to experience. The truth is
that reasoning is applied but likely not as a conscious thought process. The scientist does
this as a matter of education, training, and experience. Investigators—the good ones—do
it as a matter of intuition, training, and experience. Figure 3.7 (Chapter 3) is solely
academic and illustrates the intellectual mechanism of how crime scene reasoning
progresses. As these mental processes are at work at the crime scene, there is little doubt
that the investigation is not a scientific endeavor. Thus, the scientific method is the best
tool to ensure a successful scene investigation.
As Sherlock Holmes said [15],
In solving a problem of this sort, the grand thing is to be able to reason backward. That is
a very useful accomplishment, and a very easy one, but people do not practice it much. In
the everyday affairs of life it is more useful to reason forward, and so the other comes to be
neglected. There are fifty who can reason synthetically for one who can reason analytically.
(p. 83)
The Scientific Method, Bias, and Reasoning
45
Fi
gu
re
2.
6
Observation
Pattern
Tentative
hypothesis
Theory
Ind
uct
ive
/de
du
cti
ve/
ab
Abductive reasoning
du
cti
ve
Confirmation
rea
so
nin
g as applied in crime scene investigations.
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