Download Impressions Evidence Notes

Presentation developed by T. Trimpe 2007 http://sciencespot.net
• What is the difference between:
• Class Evidence &
• Individual Evidence?
• One of the primary endeavors of forensic scientists must be
to create and update statistical databases for evaluating the
significance of class physical evidence.
• The chances of finding class physical evidence are much greater
than individual physical evidence.
Assessing the Value of Evidence:
• The value of class physical evidence lies in its ability to corroborate
events with data in a manner that is, as nearly as possible, free of
human error and bias.
• It is the thread that binds together other findings.
• The chances of finding two identical pieces of physical evidence at a
crime scene that did not originate from the same source are low.
• As the number of objects linking an individual to a crime scene
increases, the likelihood that he/she was involved increases
dramatically.
Cautions and limitations in dealing with
physical evidence:
• The weight of significance of physical evidence is left entirely
to a jury of laypeople.
• Physical evidence may also be used to exclude a person from
suspicion.
• The task of the forensic scientist is to find as many
characteristics as possible to tie one substance with another.
• For forensic examiners, reading text books and relevant
journals is no substitute for experience.
• In a criminal investigation, the ultimate contribution that a
criminalist can make is the linking of a suspect to a crime
through comparative analysis.
Fingerprint databases:
• Integrated Automated Fingerprint Identification Systems
(IAFIS) – a national fingerprint and criminal history database
maintained by the FBI and launched in 1999.
• Once the quality of the print is deemed suitable for the IAFIS search, the
examiner creates a digital image of the print.
• Then the examiner marks points on the print to guide the search.
• The print is then electronically submitted to IAFIS.
• Within minutes, the examiner may receive a list of potential matches
and their corresponding fingerprints for verification.
DNA Databases:
• In 1998, the FBI’s Combined DNA Index
System (CODIS) became fully operational.
• CODIS Creates investigative leads from 2
sources:
• The forensic index.
• The offender index.
• The forensic index currently contains 110,000
profiles from unsolved crime scene evidence.
Based on a match, police in several
jurisdictions can identify serial crimes.
• The offender index contains profiles from
nearly three million convicted or arrested
individuals.
• Hundreds of thousands more are backlogged and
waiting for entry into the system.
Other Databases:
• National integrated Ballistics Information Network (NIBIN)
maintained by the Bureau of Alcohol, Tobacco and Firearms.
• Firearms and explosives – allows analysts to acquire, digitize, and
compare markings made by a firearm on bullets and casings.
• The heart of this database is the (IBIS) Integrated Ballistic Identification
System. Comprising a microscope and a computer unit that can capture
an image of a bullet or cartridge casing. Images are forwarded to a
regional server.
• IBIS does not definitively match a bullet to a firearm. It merely provides a
list of candidates that the investigator can follow up on.
• Database contains chemical and color information pertaining
to original automotive paints.
• Developed and maintained by the Royal Canadian Mounted Police.
Contains information on the make, model, year and assembly plant of
more than 13,000 vehicles (types). Also has a library of more than
50,000 layers of paint.
• Greatest use in hit-and-run cases.
SICAR (Shoeprint Image Capture and
Retrieval) –
• a NONgoverment database.
• Commercially available, used
for comparing and identifying
crime scene shoeprints.
• Can link a crime scene shoe
impression to a particular
shoe manufacturer.
• Tread Assist – Tire
Impressions.
What is impression evidence?
• Impression evidence can be
defined
as
objects
or
materials that have retained
the characteristics of other
objects through direct contact.
• Impressions are created when
one object is pressed against
another material with enough
force to leave an impression of
the object.
• Shoeprints, tool marks, tire tracks, bite marks,
and marks on a fired bullet are several examples
of impression evidence.
• Impressions may be found in or on many different
types of materials.
• The quality of the impression depends on:
• the object making the impression.
• the surface conditions, such as how hard or soft
it is and what type of material it is (soil, mud,
dust, concrete, grass, skin, etc.)
2-D:
• This type of impression is documented using
photography.
• Some impressions may be dusted with fingerprint
powder to be photographed or lifted with tape.
• They may also be collected using an electrostatic dust
lifting process.
3-D:
• This type of impression can be documented using
photography as well as by casting, which involves
using dental stone or a similar substance to preserve the
dimensional characteristics of the print.
Collection Methods
Investigators analyze the impression
evidence to find unique characteristics to
link shoes, tires, tools, and other objects
found in a suspect’s possession to evidence
at a crime scene.
Collection of impression evidence can be
accomplished using several methods:
Example of Shoe Print in
Bio-Foam Impression Foam
Tire Track Evidence
• Tire tracks are important in
forensic investigations and are
usually found in road accident
scenes or in the access and
escape routes of other crime
scenes.
• Tracks
help
investigators
identify the type of vehicle that
left them.
• Investigators may make ink
prints of a tire or plaster casts
of a track. They will also take
photographs that can later be
used to prove a match.
Features to analyze:
• Tread pattern.
• Width & depth of the tread pattern.
• Unique characteristics due to the wear pattern or defects.
• Tire databases are available help investigators determine
the brand and model of the tire that left the impression ,
which can be used to determine the type of vehicle that
made the tracks.
Tool Mark Evidence
• Certain defects or patterns may be left
on a tool when it is made or used, which
can be used to find matches between
evidence at a crime scene and tools or
objects found at a suspect’s home.
“Stocking Strangler” – bite mark impressions.
Tool marks can be classified two ways:
• Impressions – As a tool hits a softer surface, the shape
of the tool and imperfections in its surface may be left
behind as an impression.
• Scratches – As a tool moves across a surface, it may
leave ridges or striations behind.
NOTE: Some tool marks are a combination of both types.
Features to analyze:
• Dimensions of the impression.
• Ridges or striation patterns.
• Defects, such as nicks and chips.
• Paint chips or metal shards left on a tool.
Shoe Print Evidence
• Investigators can analyze
a shoe print to determine
its class, or the type and
brand of shoe. They will
also look for individual
characteristics, such as
wear
patterns
and
specific damages or
defects.
• Databases of shoe prints
are help investigators
determine the brand of
shoe to provide leads for
a case.
STAMP Database
Bite Mark Evidence
• Investigators can analyze bite
marks for characteristics to
help them identify victims or
suspects as well as to exclude
others.
• Marks can be left on a
victim’s skin or other objects,
such as Styrofoam cups, gum,
or foods.
• Dental records including xrays can also provide useful
information, especially when
attempting to identify a
victim.
Bite Mark Evidence Video
Features to analyze:
• Type of bite mark (human or animal).
• Characteristics of the teeth (position, evidence of dental
work, wear patterns, etc.).
• Color of area to estimate how long ago the bite occurred
(old or recent bite).
• Swab for body fluids for DNA tests.
Did you know?
The most famous incident where bite mark evidence led to a
conviction, was in the case of the notorious serial killer, Ted
Bundy. He was responsible for an undetermined number of
murders between 1973 and 1978 and was finally tied to the
murder of Lisa Levy through bites that he had inflicted on
her body.
•
•
•
•
Dental training
Licensed dentist
Special classes and seminars
Forensic Odontology certification from American
Academy of Forensic Science
• Comparison of antemortem data with postmortem data.
• Presumptive vs. positive identification.
• Presumptive = to the best of our ability to determine, this is
the person.
• Positive = we know this is the person.
•
•
•
•
Dental record comparison
DNA
Fingerprints
Radiological
• Primary (deciduous set) – 20 teeth
• Secondary (permanent set) – 32 teeth
• Maxillary set
• RU quadrant
• LU quadrant
• Mandibular set
• RL quadrant
• LL quadrant
• Incisors
• Central and lateral
• Canines
• Premolars (bicuspids)
• First and second
• Molars
• First, second and third
• Using a pre mortem x-ray and a dental chart any major
construction is marked on the dental chart.
• Using a post mortem x-ray and a dental chart features are also
marked.
• Comparative overlays of teeth angles and separations are also
used to positively identify decedents.
• Often there are bite marks that can be used to identify
perpetrators (Ted Bundy).
• Photographic study and image enhancement with comparative
study may exclude or positively identify a suspect.
• Most often seen in rape, murder, child abuse and spousal
abuse.