The Crime Scene
Chapter 2
Physical Evidence
 Physical evidence is any object that can
establish that a crime has been committed or
can link a crime and its victim or its
perpetrator.
 Forensic science begins at the crime scene.
The investigator must recognize physical
evidence & properly preserve it for laboratory
examination.
 The evidence must be kept in its original
condition as much as possible.
Securing the Crime Scene
 Secure & Isolate the Crime Scene
 First priority is medical assistance to individuals &
arresting the perpetrator.
 Ropes or barricades and guards will prevent
unauthorized access to the area.
 Every person who enters the crime scene has the
potential to destroy physical evidence.
 The lead investigator evaluates the scene &
determines the boundaries. They do an initial
walk through & develop a strategy.
 All items must be documented & photographed.
Recording the Crime
Scene
 3 methods of
crime-scene
recording:
photography,
sketches, & notes
 Ideally all 3
should be used
Photography
 The crime scene should be unaltered, unless
injured people are involved, objects must not
be moved until they have been photographed
from all necessary angles.
 If things are removed, added, or positions
changed the photographs may not be admissible
evidence.
 Photograph completely
 Area where crime took place & adjacent areas
 Various angles
Photography
 If crime scene includes a body:
 Take photos to show body’s location & position relative to
the whole crime scene
 Take close-up photos of injuries & weapons lying near
the body
 After the body is removed, photograph the surface
underneath.
 When size is significant, use a ruler or other
measuring scale
 Digital cameras allow for enhancement &
examination in fine detail.
 Videotaping a scene is also becoming popular.
Sketches
 Once photos are taken, sketch the scene.
 A rough sketch is a sketch, drawn at the crime
scene, that contains an accurate depiction of the
dimensions of the scene & shows the location of all
objects having a bearing on the case.
 All measurements are made with a tape measure
 Show all items of physical evidence
 Assign each item a number or letter and list it in the
legend
 Show a compass heading designating north
 A finished sketch is a precise rendering of the crime
scene, usually drawn to scale.
 Computer-aided drafting (CAD) has become the standard.
Rough-sketch diagram of a crime
scene. Courtesy Sirchie Finger
Print Laboratories, Inc.,
Youngsville, N.C.,
www.sirchie.com.
Finished-sketch
diagram of a crime
scene. Courtesy
Sirchie Finger Print
Laboratories, Inc.,
Youngsville, N.C.,
www.sirchie.com.
Notes
 Note taking must be a constant activity
throughout the processing of the crime scene.
 The notes may be the only source of
information to refresh memory.
 Tape-recording notes at a scene can be
advantageous – detailed notes can be taped
much faster than they can be written.
Dealing with Physical Evidence
 Once found, physical evidence must be
collected & stored in a way that preserves its
integrity for forensic comparison & analysis.
 The search for physical evidence must be
thorough and systematic, even when
suspects are immediately seized.
 A forensic scientist is not usually needed at
the scene unless the evidence is complex or
it is a major crime.
 Some police agencies have trained field
evidence technicians.
Searching the Crime Scene
 One person should supervise & coordinate.
 Include all probable entry & exit points in
search
 What to search for will be determined by the
particular circumstances of the crime.
 Examples
 Homicide
 Hit-and-run
 In most crimes, a search for latent
fingerprints is required.
Systematic Search
Collect Physical Evidence
 Physical evidence can be anything from massive
objects to microscopic traces.
 It may be necessary to take custody of all clothing
worn by the participants in a crime.
 Handle carefully & wrap separately to avoid loss of trace
evidence.
 Critical areas of the crime scene should be
vacuumed & the sweepings submitted to the lab for
analysis.
 Mobile crime-scene vehicles carry supplies to
protect the crime scene; photo, collect, & package
evidence; & develop latent fingerprints.
Collect Physical Evidence
 The integrity of evidence is best maintained
when the item is kept in its original condition
as found at the crime scene.
 The entire object should be sent to the lab.
 If evidence is found adhering to a large
structure, remove specimen with forceps or
other appropriate tool.
 In the case of a bloodstain, one may either scrape
the stain off the surface, transfer the stain to a
moistened swab, or cut out the area of the object
containing the stain.
Collect Physical Evidence
 Each different item or similar items collected
at different locations must be placed in
separate containers.
 Packaging evidence separately prevents
damage through contact and prevents crosscontamination.
Autopsy Room
 Medical examiner or coroner carefully examines the
victim to establish a cause & manner of death.
 Tissues are retained for pathological & toxicological
examination.
 The following are collected & sent to the lab:
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Victim’s clothing
Fingernail scraping
Head & pubic hairs
Blood (DNA typing)
Vaginal, anal, & oral swabs (in sex-related crimes)
Recovered bullets from the body
Hand swabs from shooting victims (for GSR analysis)
Tools for Evidence Collection
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Forceps
Unbreakable plastic pill bottles w/ pressure lids
Manila envelopes, glass vials, pill boxes
Paper bags are better than plastic…why?
Fire evidence must be kept in an airtight container
to prevent evaporation of petroleum residues
 Clothing must be air-dried & placed in individual
paper bags.
 http://www.crimescene.com/ecpi/evidence_collection.shtml
Chain of Custody
 Chain of custody is a list of all people who came into
possession of an item of evidence.
 Chain must be established whenever evidence is
presented in court as an exhibit.
 Failure to do so may lead to ? Regarding authenticity &
integrity of evidence.
 All items should be carefully packaged and marked
upon their retrieval at crime sites.
 Normally, the collector’s initials & date of collection
are inscribed directly on the article.
 The evidence container must also be marked with
collector’s initials, location of evidence, & date of
collection.
Standard/Reference Samples
 The examination of evidence often requires
comparison with a known standard/reference
sample.
 A standard/reference sample is physical evidence
whose origin is known, such as blood or hair from
a suspect, that can be compared to crime scene
evidence.
 Such materials may be obtained from the
victim, a suspect, or other known sources.
 The presence of standard/reference samples
greatly facilitates the work of the forensic
scientist.
Standard/Reference Samples
 Bloodstained evidence must be accompanied by a
whole-blood or buccal swab s/r sample obtained
from all relevant crime-scene participants.
 A buccal swab is a swab of the inner cheek, performed to
collect cells for use in determining the DNA profile of an
individual.
 Some types of evidence must also be accompanied
by the collection of substrate controls.
 Normally collected at arson scenes.
 A substrate control is uncontaminated surface material
close to an area where physical evidence has been
deposited; used to ensure that the surface on which a
sample has been deposited does not interfere with
laboratory tests.
Submitting Evidence to the Lab
 Evidence is submitted to the lab either by
personal delivery or by mail shipment.
 Most labs require that an evidence
submission form accompany all evidence
submitted.
 Enables the lab analyst to make an intelligent &
complete examination of the evidence.
 Provide a brief description of the case history so
the examiner can analyze in a logical sequence.
 The particular kind of examination requested for
each type of evidence should be delineated.
 A list of all items submitted must be included.
Death & Autopsies
 Forensic Pathology involves the
investigation of unnatural, unexplained,
or violent deaths.
 Forensic pathologists in their role as
medical examiners or coroners are charged
with determining cause of death.
 The forensic pathologist may conduct an
autopsy which is the medical dissection and
examination of a body in order to determine
the cause of death.
Estimating Time of Death
 After a human body expires there are several
stages of death.
 Rigor mortis results in the shortening of muscle tissue
and the stiffening of body parts in the position at death
(occurs within the first 24 hours and disappears within 36
hours).
 Livor mortis results in the settling of blood in areas of the
body closest to the ground (begins immediately on death
and continues up to 12 hours).
 Algor mortis results in the loss of heat by a body (a
general rule, beginning about an hour after death, the
body loses heat by 1 to 1-1/2 degrees Fahrenheit per
hour until the body reaches the environmental
temperature).
Other Specialties
 Forensic Anthropology is concerned
primarily with the identification and
examination of human skeletal remains.
 Forensic Entomology is the study of insects
and their relation to a criminal investigation,
commonly used to estimate the time of
death.
 Forensic Psychiatry is an area in which the
relationship between human behavior and
legal proceedings is examined.
Typical blowfly life cycle from egg deposition to adult fly
emergence. This cycle is representative of any one of the nearly
ninety species of blowflies in North America. Courtesy E. P.
Catts, Ph.D., deceased, and Neal H. Haskell, Ph.D., forensic
entomology consultant www.forensic-entomology.com.
Other Specialties
 Forensic Odontology involves using teeth to
provide information about the identification of
victims when a body is left in an
unrecognizable state; also investigates bite
marks.
 Forensic Engineering is concerned with
failure analysis, accident reconstruction, and
causes and origins of fires or explosions.
 Forensic Computer Science involves the
examination of digital evidence.
Crime Scene Safety
 The increasing spread of AIDS and hepatitis B has
sensitized the law enforcement community to the
potential health hazards that can exist at crime
scenes.
 In reality, law enforcement officers have an
extremely small chance of contracting AIDS or
hepatitis at the crime scene.
 The International Association for Identification
Safety Committee has proposed guidelines to
protect investigators at crime scenes containing
potentially infectious materials that should be
adhered to at all times.