The Crime Scene

SFS1. Students will recognize and classify various types of evidence in relation to the definition and scope of Forensic Science.

b. Distinguish and categorize physical and trace evidence (e.g. ballistics, drugs, fibers, fingerprints, glass, hair, metal, lip prints, soil, and toxins).

c. Determine the proper techniques to search, isolate, collect, and record physical and trace evidence.

d. Evaluate the relevance of possible evidence at the site of an investigation.

e. Organize relevant information to accurately develop and submit both scene and analysis reports.

ESSENTIAL QUESTIONS• How can you identify and distinguish

testimonial and physical evidence?• Why is physical evidence more

valuable?• How can you identify and distinguish

individual and class evidence?

ESSENTIAL QUESTIONS• What are the processes involved in

preserving and isolating the crime scene?• How do CSIs observe and document a

crime scene, search the scene for evidence, and collect and package evidence?

• What is the importance of the chain of custody?

Types of Evidence• Testimonial Evidence

– Statement made under oath– Can be direct or circumstantial evidence– Juries are heavily influenced by eyewitness

testimony– Reliability can be questionable– Hearsay is a statement, other than one made while

testifying, offered in evidence to prove the truth of the matter

• It is generally inadmissible in criminal court because it is unreliable, not under oath, and unavailable for cross-examination

Testimonial Evidence• Witnesses are more accurate in remembering

characteristics such as sex and hair color rather than age, height, and race– Witnesses that are physically similar to offender

will be more accurate– Victims of serious crimes are more accurate– Presence of a weapon sharpens focus; stress

narrows focus

Testimonial Evidence• Children usually don’t remember as well as

adults– Testimony of children is more easily affected by

interviewing techniques– Older adults, however, have dulled vision and

hearing, resulting in less accuracy• Learning disabilities, head injury,

drugs/alcohol weaken memory and recall

Testimonial Evidence• Eyewitnesses are better at answering

questions about the event rather than the offender’s description– Open-ended questions get better answers

• Most known cases of an innocent person being convicted is because of mistaken eyewitness identification

Types of Evidence• Physical Evidence

– Any material or object establishing a fact based on its physical characteristics

– Can be direct or circumstantial– Generally more reliable than testimonial evidence– Physical evidence is primarily processed by

comparing a questioned/unknown sample to a control/known sample.

– Trace evidence is evidence that occurs when different objects contact one another.

Types of Physical Evidence• Individual Evidence

– Linked to a unique, single, specific source– Examples include fingerprints, DNA, broken

pieces, handwriting

• Class Evidence– Has characteristics common to a group of similar

objects– Examples include clothing, carpet, food, hair– Can increase the probative value by using several

pieces to link a suspect to a crime

Physical evidence is valuable because it can…

• Prove a crime has been committed and set the scene for the investigation

• Support or refute witness testimony• Link a suspect with a victim or with a crime

scene• Determine the identity of people associated

with a crime• Allow investigators to reconstruct a crime

On scene…

By gathering information at a crime scene, Crime Scene Investigators can develop links among the evidence, victim, crime scene, and perpetrator.

Those links can help them reconstruct the sequence of events, the modus operandi, and motive.

Preserving and Isolating the Crime Scene

• Role of the First Responder– Determines the nature of the crime– Gets assistance for the injured– Detains and/or arrests suspects– Detains and isolates witnesses– Secures the crime scene, ensuring all evidence is

contained within the enclosure– Record all activity– Remain on site until further staff arrives

Preserving and Isolating the Crime Scene

• Role of the Medical Examiner–Note the body’s condition–Estimate time of death–Protect physical evidence from

tampering and destruction

Preserving and Isolating the Crime Scene

• Role of the Investigator– Interviews victim(s), witnesses, police on

the scene, other specialists– Responsible for the management of

information given to the press– Discuss the evidence with the prosecutor’s

office to determine the legal direction of the investigation

Observing and Documenting the Scene

• Investigators should examine the scene to…–Find possible items of evidence–Identify entry and exit–Consider what happened–Outline how the scene should be

handled

Observing and Documenting the Scene

• There are three primary methods of documenting a crime scene–PHOTOGRAPHY and VIDEO RECORDING–SKETCHES–NOTES

Observing and Documenting the Scene

• PHOTOGRAPHY and VIDEO RECORDING– Captures important details not immediately

observable– Scene must be photographed before touching or

moving any evidence– Should include close-ups of evidence, views

through the eyes of the witness and at various angles

– Ruler should be used for scale– Video recordings should begin outdoors and move

indoors

Observing and Documenting the Scene

• SKETCHES–Give perspective to the photographs–Rough sketches are done in situ; finished

sketches are completed using CAD technology

– Include measurements, scale, relative placement of all important details in the crime scene

–Should also include artist’s name, date/time, reference points, and a legend

Observing and Documenting the Scene

• NOTES– One of the most important parts of

processing the crime scene– Forces investigator to be more observant and

enhances memory of details– Should include measurements,

names/dates/times, locations, environmental conditions, description of crime

– Audio recording can be helpful

Searching the Scene for Evidence

• The investigators are looking for anything that should not be there

• Anything that might carry trace evidence should be collected

• Special lighting may be used to spot invisible body fluids

• Large search areas may be searched with multiple investigators

Search Patterns

Collecting and Packaging Evidence

• All evidence is bagged and labeled individually

• Reference samples should also be collected

• Evidence should be sealed with tamper-proof tape

Maintaining the Chain of Custody

• Is the chronological documentation “paper trail” showing the seizure, custody, control, transfer, analysis, and disposition of evidence, physical or electronic.

• The idea behind recording the chain of custody is to withstand legal challenges to the authenticity of the evidence.