The Biological Crime Scene
It’s Not Just About DNA
Locard: "Every Contact Leaves a Trace".
Blood at the Scene is the most visible
example of the Locard Exchange Principle
Biological Evidence

Think about the totality of evidence one might expect at a crime scene:

impression evidence,

bloodstains,

bullets, etc.

Trace evidence
 All are important,
 Scene investigators often fail to find one or more, simply assuming not present.

Not unusual. It is expected because of the crime circumstances.

Ballistics evidence is not expected and should not be present if the crime did not
involve a shooting.
 Failing to locate biological evidence, however, has a different “feel” because of the lofty
stature of DNA. BECAUSE it can identify someone.

Crime scene investigators and scientists focus FIRST on finding biological
evidence, so much so that their rallying cry might well be, “Find DNA and you’ve got
your perp.”

This works because DNA profiles from biological evidence collected at the crime
scene are uploaded into an FBI maintained database –

CODIS (Combined DNA Indexing System). CODIS: Once in the system, scene
profiles can be matched to other crime scenes, convicted felons, arrestees or to
identify missing persons.
 DNA is coveted as evidence from both investigational and legal
perspectives.
How Much Biological Evidence
Is at a Crime Scene?
At some scenes, investigators fail to find biological evidence.
 It is probably safe to say that every crime scene involving people probably had
biological evidence … means that investigators have been missing biological evidence
for a long time.
 Reality: In homicide cases: Only 5-10% yield of biological evidence
 The fact is, they missed it.
Consider this
 Anyone entering a room brings something of themselves with them. When they
leave the room, they leave something behind. Certainly, whatever is left behind might
be difficult or even impossible to find.
 But new technology on the nebulous horizon might be able to find it.
Example Case:
 But this is the murder weapon AND
biological evidence is present. By
definition, biological evidence must be
present. Many scene investigators will fail
to collect the brick, and others might …
just to be safe.
 Both investigators might believe the
brick holds no evidentiary value. The
forensic scientist in the laboratory could
have a different opinion based on finding
shed skin cells lodged in the its crevices,
 A technique that has not yet
found its way into the field.
 Investigator finds young deceased
male on the floor. no head hair and a large
contusion on the side of his head.
 No obvious bloodstain impact
spatter.
 No apparent active bleeding: only
a trickle of blood on the deceased’s
cheek,
 No blood droplets on the floor …
no sign of a struggle.
 Outside the back door on the pavement
is an old, broken brick with rough edges.
The message:
… Location is not particularly unusual …
should not any raise suspicion that it might  Biological evidence is always
be the murder weapon.
present.
 Picking up the brick and casually  Unfortunately, we do not yet have the
examining it reveals nothing except,
technology to detect all of its traces
perhaps, some dirt: certainly no hair
and there is no obvious blood or skin.
What is Biological Evidence
 “Common Examples” … examples of forensically
important biological evidence occur more than others.
 Others also occur commonly … fingerprint
residue or sloughed off cells … investigators do not
think of them as common biological evidence;

Fingerprints: not thought of as biological
evid

Sloughed-off Cells: not visible.
 The reason is that the value of fingerprint residue
is thought of in terms of its friction ridge detail.

Fingerprints contain biological substances,
some of which has current or potential forensic
value: fatty acids, proteins and cells (DNA).
 Thinking of fingerprint residue a little differently
may pave the way for it to become more valuable as an
example of biological evidence.
Common Examples
Blood – Human & Animal
Semen
Saliva
Urine
Feces
Vomit
Hair
Fingerprint residue
Sloughed Off Cells
Not So Common Examples
Bacteria
Plant material
Pollen
Viruses
Finding Biological Evidence
 Critical elements of the macro and micro scenes
 Bloodstain patterns, droplets, etc
 Pollen, bacteria, etc.
Arguably leader’s most important responsibility, given the critical importance of
DNA, is to find and collect anything having biological properties. This is a top
priority.
 Not an easy task:
 Is it everywhere
 Represents only a small fraction of the totality of the biological spectrum
present.
 With the possible exception of a bio-terrorist event, the most probative biological
evidence comes from people.
 Who live where the crime occurred,
 visitors where the crime took place but had nothing to do with the event,
 public officials who investigate the scene and the
 criminal who commits the crime.
 Challenge: Find important probative biological evidence among all present.
 Successful searching requires : All senses, ability to think creatively, common
sense … Luck, too.
The Cognitive Tools





The Evidence Analysis Cascade
Your Brain
Logical & Critical Thinking
Experience
Understanding the Science and Technology
The investigator’s mission is
“Never Miss Anything Probative”
 The successful search for biological
evidence, any evidence for that matter,
requires special attributes and diligence.
 Acquiring the appropriate expertise is
not a matter of attending a workshop that
teaches how to use an ALS to locate
evidence: semen, saliva or urine or how to
employ presumptive chemical tests to
classify an unknown stain as blood.
 The Intellectual Approach is the Key to
Success
 Appropriate scientific education,
experience,
 Brains that think creatively and
skeptically,
 Understanding the underlying science
behind the technology and
 Being aware of and knowing how and
when to apply technology … the scene
investigation is poised for disaster.
Locating Critical Biological Evidence

Historically:

Blood: Chemical tests commonplace 100 years ago to
determine whether reddish stains might be blood.

Semen: In the 1950’s they used enzymatic tests (acid
phosphatase test) to determine whether a crusty stain might
be semen.
 Modern Techniques use technology

High intensity light sources for the most part have
replaced touch for locating latent biological stains. The
historical technological sequence started with UV lights
followed by lasers and then alternate light sources (ALS).
 ALS’s, make locating biological evidence easier,
especially semen, saliva, urine and blood.

Scene-forward immunological tests have entered the
forensic arena, which can confirm whether a stain is human
blood, semen or even saliva.
 Regardless of advances in technology, the most important
tool the scene scientist possesses is the brain … critical thinking
(the brain) marries technology.
Brain is best and only way to find biological evidence.
•
•
•
•
•
•
•
•
Eye
Brain
Touch
Hi-Intensity light
ALS
Chemical Tests
Enzymatic Tests
Immunological
Tests
The Scene & the Forensic Laboratory
The Evidence Analysis Cascade
The Evidence Analysis Cascade
Gross Visual Examination
Stereomicroscopy
Impression
Trace
Evidence
Evidence
Pattern
Scrapping Tape lift
Presumptive TestingPattern Analysis Analysis Soil/Paint/Glass
Hairs
Fibers
Tactile Chemical Enzyme
Immuno.
ALS
Analysis Testing Testing
Chromat.
Confirmatory Testing
Biological
Evidence
Confirmatory Testing
Species Immuno Microcrystal
Testing Chromat. Analysis
Genetic Marker Testing
DNA
Instrumental
Analysis
Microscopy
Lectins
Pattern
Analysis
Red = Common Techniques
Blue = Lab only Techniques
Commonly Occurring
Biological Evidence
Blood
What Is Blood?
Blood
Cells
Liquid
Red Blood Cells Plasma
White Blood Cells
Serum
Forensically Speaking:
What is Blood?
Blood
Complex
Connective Tissue
Cells
Plasma
Salts
Hormones
Antigens
Drugs
Antibodies
Enzymes
Blood Group
Substances
Individual
Specific
Antibodies
White Cells
Red Cells
Genetic Markers
HLA
Antigens
Blood Group
Antigens
DNA
Isoenzymes
Forensically Critical
Information from Blood
Drugs of Abuse
Prescriptions
Genetic Markers
Identification
Psychological Behavior
Disease Susceptibility
Ancestry
Racial Identity
Sexing
Individual Identity
DNA
Profiling
Antibody
Profiling
On-scene testing for blood
Could It Be Blood?
Presumptive testing …
 A test helps an investigator decide whether a particular stain
MIGHT be blood and thus have investigative value.
A presumptive test, then, is a “maybe” test, one where a positive
result means that the stain might be blood. These are not
confirmation tests.
Other tests are needed to confirm whether the biological material is
present.
The Unaided Human Eye
 The eye:
 Oldest presumptive test.
 Not always red.
o Dried blood can be red, brown, yellow, green or black,
o Understanding the conditions under which these transitions occur is
important.
 The eye, not a stand-alone-instrument because connected to brain.
 Interprets color and then determines (presumptively) that red substance is blood.
 Evaluating it in the context of our experience, a
 Experience is what is really what is being tested.
 Not a confirmatory test,
 Coupling observational skills with experience narrows the range of possibilities.
 A good first approach, but technology can enhance the likelihood of finding blood.
 Experiences are not infallible or applicable to all situations, and not the most reliable
indicator of the ground truth.
 For an experienced scene investigator, observing something red having the appearance
of blood spatter means that it “looks like” blood.
 Does not mean that it is blood.
 Certainly the investigator’s experience is important, but certainty is not the test of
certitude.
 Being “certain” that something is what one thinks it is does not make it so.
The Aided Human Eye –
Alternate Light Sources (ALS)
 Light enhances ability to “see” evidence where it normally would be invisible. Oblique
lighting is an example of how light helps find impression evidence.
 Flashlight is an important on-scene tool,
 Recent developments in light technology – lasers and alternate light sources – have produced
portable, high intensity instruments with tunable wavelengths that can highlight some categories
of evidence better.
 Useful example is ALS, which has proven to be a versatile resource for scene
investigators because it enhances the ability of the human eye to “see” better.
 The molecules that comprise the evidence absorb specific wavelengths of light. When this
happens, the evidence will appear dark.
 If the molecules lose energy, they might be seen as light – fluorescence. This is a topic we
discussed in Part I of this lecture series. This happens because an ALS has a tunable
wavelength dial that offers the scene scientist choices depending on the scene situation.
 Tunable wavelengths are typically not available on a normal flashlight.
Using Light Sources
To Find Biological Evidence
The Electromagnetic Spectrum
Using Light to Find Biological Evidence
Ultraviolet Region
190-290
290-400
Short
wave
Long
wave
Visible Region
400-455
455-492
Violet
Blue
492-577
Green
577-597
Yellow
597-622
Orange
622-700
Red
Infrared Region
Blood Absorbs Light
Appears Dark
>700
IR
Detecting Blood with the ALS
Blood on Light Colored Surfaces
 “Tricks”, depending on the surface on which the blood lies.
 For example, the 415nm (and 450nm) setting on the ALS (violet
light) makes the blood appear darker on light backgrounds,
 Enhances apparent visibility.
 Dried blood absorbs light at that 415nm,
o Why it appears darker instead of reddish or reddish
brown.
 The increase in contrast between the blood and the surface forces
the eye into a more favorable region of the electromagnetic
spectrum.
Blood on dark surfaces

Dark Surfaces
 415nm approach does not work
 Making the blood appear darker is counterproductive because the contrast
between the surface and the blood is diminished
 Difficult to see and easily missed, … forces scene investigators to choose
alternative methods.
 Subtract background:
o Use light of different wavelengths (colors) … ALS.
o If successful, blood will appear dark against a lighter background.
 An example is blood on a red wall.
 Oblique lighting on shiny surfaces
IR light
Differentiating Food
Stains From Blood
 Differentiating food from blood @ scene
prevents the crime laboratory from having
to analyze superfluous and irrelevant
evidence.
 Blood absorbs at 415nm …
 Does not fluoresce under long-wave
ultraviolet light (300-400nm – both
settings on an ALS).
 Tomato-based foods may or may not
absorb light at 415nm (usually less so than
blood) …
 Give blue-white fluorescence and a
yellow or yellow-orange fluorescence
under long-wave UV light.
Long-wave UV Light
On Wall
Blood
Ketchup
Stain on the left = bloodstain
Stain on the right is a ketchup stain.
• The blood absorbs the light, which is why it
appears darker.
• The ketchup has a blue-white fluorescence.
Infrared (IR) Cameras
Combining Searching and Archiving
Blood absorbs in the infrared, which makes it appear dark,
 Can visualize blood on dark backgrounds that do not absorb in IR
 Sometimes on dark, shiny surfaces.
 In the past,
o Delayed for film processing
 Made on-scene usefulness problematic because it took time before
the investigators knew whether the infrared light had “found” blood.
o Used show blood patterns on dark surfaces where it was known to be
present.
o Not a mechanism for finding difficult to see bloodstains AT THE
SCENE during the investigation.
 Digital IR camera and the ALS are valuable on-scene partners
 Tools to help locate dried blood on difficult surfaces.
 Digital cameras have characteristics different than film cameras simply
because they the LCD viewers allow one to “see” the blood in-situ.
Detecting Blood Using
An IR Camera
Instantaneous peek at dark
surface … does not absorb IR light..
Camera expands an investigator’s
sight range into the real-time near
infrared, … IR digital camera is
indispensible tool for on-scene
investigations. Even when the ALS
is of little or no help.
Importantly, too, the LCD IR
image can be photographed and
included in the crime scene unit’s
case file.
Legend: White arrows point to bloodstains
The IR highlighted stain can be
tested with presumptive chemicals or
tested using immunochromatographic
cards to ascertain whether it is blood
or human blood respectively.
The stains on the carpet in
photograph were invisible to the
naked eye and to the settings on the
ALS – the ALS could not effectively
subtract out the background
ALS Wavelengths
Applications to Finding Biological Evidence –
MiniScope 400
Evidence Type
ALS Settings
Goggle
Camera Filter
Bone
Teeth
Fingernails
455/CSS/515
Orange
Orange
Body Fluids
Dk Surfaces
“ w/crust
CSS
UV
White/oblique
Orange
Clear/Yellow
Clear
Hair
untreated Blk
White/oblique
treated-red/bld 415/CSS
Clear
Yellow/Orange
Blood
Clear/Yellow
415, 455
1-2 Orange
None
None
None
Yellow/Orange
None
Choosing a Goggle Color
Matches Wavelengths
Color Range
Long wave UV
Violet
Blue/green
Green-red
------
ALS Setting (nm)
300-400
515-445
455-515
536
CSS
Goggle
Clear
Yellow
Orange
Red
Orange
http://www.evidentcrimescene.com/cata/light/light.html
Detecting Blood
@ the Scene
1862
Chemical Presumptive Testing
 Chemical tests that react with blood were developed in the mid 19th century.
Needed a method to know whether unknown stain might be blood
Chemistry narrowed the range of possible substances by approximately 95%.
 Positive chemical test means that there is approximately a 95% chance
that the unknown stain is or contains blood.
 Many reddish or dark stains at a crime scene are not blood.
 Example is stain from the spray of a shaken CokeTM can on a dark wall.
 Each works on the same principle.


Two categories: Colored Dyes or Luminescence.
 The former include a range of dyes that turn color in the presence of hemoglobin, a
protein component of blood, and a peroxide – hydrogen peroxide is the most commonly
used peroxide.
 These reagents are available commercially and include a vast array of choices:
Common Presumptive Test Reagents
phenolphthalin (Kastle-Meyer)
leucomalachite green (LMG)
Luminol (BlueStar)
3,3’,5,5’-Tetramethylbenzidine (TMB)
leucocrystal violet (LCV)
o-tolidine
Benzidine: Carcinogenic
o-toluidine
hydrogen peroxide: Bubbles
Blood – Presumptive tests
General Considerations
Step 1: Oxygen free radicals cleaved from peroxide group
Heme
Fe+++
Heme
Fe++
2H2O2
2O· + 2H2O
Step 2: Oxygen free radicals react with reduced dye
O·
+ Chemical reduced
Presumptive test detects oxidized organic dyes
chemical
oxidized (Colored)
Kastle-Meyer Test for Blood
Most Common Lab & Scene Test
 One step
Kastle-Meyer Test
Commonly Used Presumptive Test for Blood
• Lightly moisten swab with distilled
water
– Ensure no excess of water
• Dissolve stain onto tip of swab
• Add drop of ethanol
• Add drop of KM reagent to stain
Cotton
Swab
P
– color change at this point: false positive
• Add 3% H2O2
• Observe Pink Color
– KM positive
Also known as the phenolphthalein test
 All reagents added together
 Considered to be most
sensitive
 Doesn’t allow for
identifying false
positives
 Two Step
 Reagent added to the stain
 Peroxide added last
 Three Step
 Alcohol added first
 Reagent second
 Peroxide last
Blood Reacting Chemicals that Luminesce
 Other category are chemicals that react with hemoglobin and peroxide but instead
of turning color, they luminesce: …

Chemiluminescence.
 Luminol, BlueStarTM and fluorescein, is used primarily at crime scenes
where clean-up is suspected.
o Luminol and fluorescein have enjoyed a long forensic history, but
BlueStar is a recently available formulation for which claims of greater
and longer luminescent intensity exist.
 BlueStar … two formulations … one for on-scene use … training. Since the
reagent is expensive, the training formulation is a less expensive version but its
manufacturers warn it will destroy DNA.
 The on-scene and more expensive version supposedly does not destroy DNA.
 Luminescence produced can be dramatic
BlueStarTM
The Luminol (BlueStar) Procedure
 Darken room or area as adequately as possible. Sometimes covering windows,
door areas, exit lights, etc, with black plastic bags will suffice.
 Spray suspect area with 2% 5-sulfosalicylic acid and allow to dry.
 Sulfosalicylic acid fixes the proteins in blood by denaturing them
 Set camera on tripod, set aperture to “bulb,” turn off lights and take photograph of
scene using a 2 minute exposure. Check that photo is not over exposed. If over
exposed, adjust shutter speed.
 If exposure is adequate (see scene detail in photograph), trip shutter and spray area
with BlueStarTM. Allow luminescence to develop.
 When fluorescence begins to fade, spray the area again. Continue this process for
the entire two minutes.
 Then trip the shutter and observe the photograph.
Hemascein
Hemascein®, a non-luminol formulation, designed to
Qualitatively reveal latent bloodstains at a crime scene.
How Hemascein Works
Hemascein® detects latent bloodstains
using a novel fluorescein
as active component
 Area suspected of containing latent bloodstains sprayed
with Hemascein® using ABASpray™.
 Hemascein® reagent is reduced by hydrogen peroxide
(colorless) and then oxidizes fluorescein.
 Fluorescence comes after excitation an ALS
 Use ALS between 415 and 480 nm.
 After locating suspect blood, test for human origin
using immunochromatographic test.
 Evidence swabbed and transported for DNA analysis.
http://www.abacusdiagnostics.com/howitworks.htm
So Many Choices: What to Use When?
 The choice of which to use and when is important.
Scene where an informant says that individual had
been murdered years earlier.
 Finding the blood visually or even with an ALS might be fruitless.
 Maybe the original scene had been remodeled or repainted.
 The team leader needs to decide how to approach the problem.
 After an exhaustive but unsuccessful search for visible blood, the team leader
might discuss the following with the team:
 Should spray using BlueStarTM ?
 Can the team darken the room sufficiently?
 OR Should use a reagent that forms a color, such as leuco crystal violet OR
KM.
 Suppose investigation based on informant’s information that the room had,
been painted to hide blood,
 Consider possibility of finding the blood “under” the paint and discuss
how to accomplish that.
 One consideration is spraying with BlueStarTM.
Confirming Human Bood
Lateral Flow Immunochromatography
Rapid technique for identifying
small amounts of specific molecules.
 Forensic application largely used to
identify blood, semen, saliva and
urine.
 Can be conducted on-scene, BUT
reagents must be purchased
commercially, which raises the
per/test cost significantly.
 Not a presumptive test:
 Specifically identify unknown
stains as human blood
 Some cards cross react
with ferret blood,
 Semen or saliva (identify
salivary amylase).
 Tests purchased as testing kits,
 Must pass quality tests for
sensitivity and specificity.
“Immunochromatography strip test, or namely lateral flow test, is
a simple device intended to detect the presence or absence of
the target analyte.” It’s a form of immunoassay. Well-known
examples are in-home pregnancy tests.
http://www.creative-diagnostics.com/Colloidal-Gold-Lateral-FlowStrips-Development.html?gclid=CMCC8-ry9LUCFY6e4Aod1lsA1Q
Immunochromatographic Cards
 Problem with immunochromatographic cards, especially those from Abacus and
OTEB is that they suffer from what is known as the Hook Effect.
 Happens when testing overly concentrated samples of human blood
 False negative test,
o Incorrect and potentially misleading result obtained.
o RSID cards do not demonstrate a Hook Effect
 When the Hook Effect occurs, sample must be diluted and re-run.
 Quickness, ease-of-operation, specificity and sensitivity of these
immunochromatographic cards makes it tempting to avoid the traditional chemical
tests entirely.
 If cost is not an issue, this might be a best choice because these tests confirm the
presence of human blood in a single test.
 Used immune-card and/or stain extract can be submitted to the laboratory for DNA
analysis,
 Should save the laboratory time in selecting certain scene stains from submitted
crime scene samples for DNA analysis,
 Laboratories normally prefer to extract the samples
Immunochromatographic Cards
Employing immunochromatographic cards exclusively
 Mistake, if all blood tested turns out to be
nonhuman.
 Negative test typically means that human blood is not
present.
 False negatives occur with highly concentrated
blood extracts … because of the Hook Effect.
 Exception is the blood test by RSID which has no
Hook effect.
 True negative occurs when there is insufficient
human blood present; all tests have limits of
sensitivity.
Of the immuno-cards available, the Abacus Diagnostics
card for blood is the more sensitive;
 HemaTraceTM card detects lower amounts of
blood than the RSID card.
Investigators
 Need to be aware of nuances among products
 Should test cards … for sensitivity and specificity
as part of the validation of a comprehensive quality
assurance program.
Used with Permission from Dr. Reena Roy
Penn State University
Touch DNA
Common Buzzword in Modern Investigative Forensics
Touch DNA
 Cellular material is biological evidence with DNA.
 Perpetrator holds a weapon or picks up an object with
an ungloved hand, cellular material transfers from the hand
to the object.
 Much modern forensic DNA analysis involves what has
become known as “touch evidence.”
 All biological evidence must be considered from the
perspective of its location at the scene, its pattern as well as
its donor.
Touch DNA vs Low Copy Number (LCN) DNA
 Touch DNA is not Low Copy Number (LCN) DNA. LCN DNA profiling allows a very
small amount of DNA to be analyzed, from as little as 5 to 20 cells.
 Touch DNA testing involves analyzing “normal” amounts of DNA
 Humans shed tens of thousands of skin cells each day, and these cells are
transferred to every surface our skin contacts. When a crime is committed, if the
perpetrator deposits a sufficient number of skin cells on an item at the scene, and that
item is collected as possible evidence, touch DNA analysis may be able to link the
perpetrator to the crime scene.
 Touch DNA has been successfully sampled from countless items including gun
grips, steering wheels, eating utensils, and luggage handles, just to name a few.
 However, since Touch DNA is usually deposited in smaller amounts than the DNA
found in bloodstains or other body fluids, it is more difficult to obtain DNA profiles from
touch DNA samples.
 The key to obtaining successful Touch DNA results depends on recognizing items
which may be suitable for Touch DNA analysis and using the sampling technique
that will recover the highest number of skin cells.
Touch DNA
Potential Evidentiary Value
• Consider the potential evidentiary value of the DNA.
 Account for the relationship between the victim and the
suspect (if one exists),
 Consider any possibility of “innocent transfer” of DNA
that may have occurred before the alleged crime.
 If suspect is a family member, and either lived
with, or had recent contact with the victim,
o Finding suspect’s DNA on the evidence may be
of limited probative value.
 Touch DNA can easily be transferred throughout the
household via day-to-day interactions, contact with
furniture items/bedding, or through the laundry.
Collection Methods
Thinking Though Where The DNA Is
 “Swabbing method”,
 Surface of item is rubbed with a cotton swab to collect possible cells.
 This method preferred for hard items such as glass or plastic.
 “Cutting method”
 Used for soft items, such as clothing, in which fabric from areas of interest is cut to collect
possible cells.

“Scraping” and “Tape Lift” methods
 Surface of soft items (such as clothing) are either scraped with a blade, or sampled with a
small piece of tape, to collect possible cells.
 Larger surface area can be sampled.
o An increase in surface area increases the number of possible cells recovered;
therefore, increasing the chances of obtaining a DNA profile.
 Ideal in situations where the scientist can locate areas on the item which are most
likely to contain the perpetrator’s skin cells.
o Clothing left at scene by the perpetrator
 Pressure points on the clothing such as the interior neck of a shirt or the
band inside a hat, are excellent candidates for these sampling methods.
 Sexual assault case where victim’s clothing removed by the perpetrator,
areas such as the waistband may contain sufficient cells belonging to the
perpetrator to produce a profile.
Thinking Through Evidence Collection
 Sexual assault by a stranger, finding the suspect’s DNA anywhere on the victim’s clothing
may have evidentiary value.
 Gather as much information from victim as possible (if living),
 Attempt to recreate the events if the victim is deceased.
 If the victim’s pants pulled down, then the investigator and forensic scientist
should consider sampling areas for Touch DNA where one would envision that the
suspect would have grabbed during the assault.
 Finding the suspect’s DNA on the victim’s clothing, and in certain areas of the
clothing, may help corroborate the victim’s version of events and help address the
allegations in question.
 Attempt to collect clothing of deceased individuals
 Collect samples from the clothing prior to the deceased being removed from the scene.
 Collecting clothing at the scene PLUS optimal preservation allows obtaining
Touch DNA at a later date, even if it’s not initially indicated to be present at the crime
scene.
Channeling Information
 Provide lab scientist with case background information in order to receive the best
advice on the potential value of DNA evidence
 Crime scene photos can be quite useful.
 Lab scientist should have appropriate questions/suggestions for the investigator to
answer or consider.
Limitations of Touch DNA
 Touch DNA sampling methods, and DNA processing procedures are very sensitive.
 Detecting contamination from law enforcement personnel or sampling investigator
 Even when appropriate PPE is worn.
 May be necessary to obtain elimination samples from key personnel in the case where foreign DNA
profiles are obtained that cannot be attributed to a suspect or the victim.
 Also an increased chance of obtaining mixed DNA profiles containing DNA from individuals that
may have come into contact with the victim/evidence item near the time of the crime.
 Contributors to these mixtures could include the victim’s spouse or children
 What does unexplained DNA mean?
 Foreign male profile from a Touch DNA sample may be obtained from evidence pertaining to a
female victim.
 If the male DNA profile doesn’t match the suspect in question the investigator needs to
consider its relevance to the case.
 The foreign profile could from the true perpetrator and the original suspect could be innocent.
 DNA profile could be from adventitious transfer from crime scene personnel, first responders,
laboratory analysts, or crime scene equipment such as fingerprint brushes.
 Need to evaluate and address these questions before moving forward with the investigation.
 Some evidence items are also not recommended for the collection.
 Severely degraded DNA - moldy clothing
 Samples exposed to extreme environmental conditions
 Weapons left outside for months or years, have been washed, or are heavily soaked in the
victim’s body fluids.
Items likely touched by many people: public pay phone or store counter.
Touch DNA Recommendations
for the Crime Scene
 It is standard practice for crime scene personnel to wear Personal Protective
Equipment (PPE) such as gloves, face masks, hair nets, and sometimes whole body
suits.
 When collecting potential Touch DNA items at a crime scene it is extremely
important that as much PPE as possible is worn so as to limit the possibility of
contamination via exposed skin, shed hairs, sweat, or saliva.
 It is not uncommon to detect DNA profiles from Detectives, Paramedics, and
Medical Examiners on evidence from cold cases and it is important that extra
precautions be taken at the modern day crime scene.
J Assoc Crime Scene Reconstr. 2012:18(1)
Scene Precautions for
Collecting Touch DNA
Avoid speaking over evidence items (even if wearing a face mask).
Collect evidence with disposable forceps (rather than gloved hands)
Place each item in separate bag.
Dust for prints using single-use brushes and small disposable aliquots of
powder
To avoid cross-contamination.
Wet/dry swabbing method is commonly used at crime scenes.
 Be careful of scrape or tape lift methods because of increased probability of
contaminating the evidence/sample with exogenous DNA
Increased potential for loss of the sample in an uncontrolled
scrapping.
Also added risk of the investigator being cut by scalpel.
Touch DNA items that may benefit from sampling with the scraping
or tape lift method should be collected and sent to the forensic
laboratory to be sampled in a more sterile environment.
Where to look for DNA Evidence
Source: https://www.ncjrs.gov/pdffiles1/nij/bc000614.pdf
Controlling Contamination
Control Contamination:
Ensure scene safety and evidence integrity.
 Limit scene access to people directly involved in
processing
 Follow established scene entry/exit routes
 Designate a secure area for trash and equipment
 Use Personal Protective Equipment
 Clean or dispose of tools/equipment and PPE
between evidence collections and scenes
 Utilize single use equipment when collecting
biological samples
Personal Protective Equipment
Disposable gloves
Masks
Eye protection
Provides a barrier to keep biological or chemical
hazards from contacting the skin, eyes, and
mucous membranes and to avoid
contamination of the crime scene
Swabbing for Touch DNA
 Wear appropriate PPE
 Moisten swab with minimal
amount of distilled water (1
drop)
 Shake off excess
 Swab the area
 Rotate swab to collect entire
surface
 Maximize swab coverage
 Try not to re-use areas of
swab
 1 swab/area (6” of area)
 Irregular or grained
surfaces
 Swab with grain
 Move swab back & forth,
rotating swab surface so that
new surface is continually
collecting sample.
 Resample area with dry swab
 Air dry all swabs
 Place swabs into appropriate
paper swab container
Bode SecurSwab™ DUO-V Swab System
DNA from Property Crimes
General Checklist
 Identify visible stains first
 Easily Identify biological evidence. Will likely yield best results
 Identify areas that may provide probative evidence when swabbing
 Areas not touched by victim
 Areas of forced entry
 Identify items that were not at the scene prior to the crime
 Water bottles, cigarette butts, etc. that may have been left by the
suspect
 Gather elimination samples
 Victims, other residents/ users of the property (i.e. family/
roommates)
Collecting From Stains & Other
Biological Sources
 Cut stain and place into appropriate
paper/cardboard evidence container
 Crusty blood on various surfaces
 Swab or scrape
 Swab
o Moisten swab
appropriately (minimal
amount of water and
follow preceding
instructions
 Scrapping
o Scrap with sterile
scalpel blade into paper
fold (druggist’s fold)
o Include scalpel blade in
packaging
o Scrape clean area of
substrate as a control.
 Bone, skin, teeth, nails
 Collect carefully & place in
paper/cardboard container
 Blood/sebum residue on glass
 Check for ridge detail
 If present process as for
fingerprint
enhancement/preservation
Joe Blozis: Evid. Tech. Mag. Sept/Oct 2012, pg 8-13.