Chapter 2
Processing the Crime Scene
• Forensic Science begins at the crime scene
• Investigators must recognize physical evidence, collect the evidence, and properly store and preserve the evidence
• Physical Evidence – any and all objects that can establish that a crime has been
committed or can provide a link between a crime and its victim or a crime and its
Processing the Crime Scene
• It is crucial that one is able to distinguish and ignore all the items that are not relevant to the crime.
• Physical evidence achieves its optimum value when its
collection is performed with selectivity governed by the knowledge of what occurs later in the crime laboratory!
Processing the Crime Scene
• CSI and Crime Labs do not solve crimes; they provide evidence for the police and investigators!
Processing a Crime Scene
1. Secure and isolate the crime scene
2. Record the scene
3. Conduct a systemic search for evidence
4. Collect and package physical evidence
5. Maintain a chain of custody 6. Obtain standard/reference
samples
7. Submit evidence to the laboratory
Secure and Isolate the Crime Scene
• Responsibility of first officer to arrive on the scene of a crime to preserve and protect the area to the greatest extent possible
• First priority is to obtain medical assistance and arrest perpetrator
• Next, efforts should be made to exclude all
unauthorized personnel and isolate area; every person that enters the scene has potential to destroy evidence
• Determine boundaries and establish the
perpetrator’s path of entry and exit; crime scene size will depend of locale of scene, size of area, and victims and suspects
Record the Scene
• There is a limited amount of time to permanently record the crime scene in its untouched state
• Recording the scene is necessary to present in trial and delineate the location of evidence
• Three methods of recording a crime scene:
– Photography – Sketches
Record the Crime Scene
• Photography– Unless there are injured parties, objects must not be moved until they have been photographed from all angles. If objects are moved, photographs may not be admissible in court – unless recorded in notes.
– Items to be photographed:
• Area in which the crime took place and all adjacent areas • Points of entry and exit from various angles
• If indoors, the entire room and wall area as well as adjacent rooms • A body’s position and close up depicting injuries and near by
weapons; once the body is removed, the area under the body should be photographed
• Physical evidence position and location as well close up (a ruler or other measuring devise may be used as a point of reference)
• Videotaping with sound is also a popular method of recording a crime scene
Record the Scene
• Sketches
– Rough sketch of the dimensions of the scene showing the location of al objects
– The dimensions of objects in the sketch are determined by two
fixed point – usually the walls of the room
– Finished sketches are usually completed with drafting tools (CAD)
Record the Scene
• Notes
– Detailed written description of the scene with location of items of
physical evidence
– Time of discovery of evidence, by whom, how and by whom it was packaged and marked, and the disposition of the item after it was collected
– Notes may be the only written
record to refresh the memory of the investigators
Conduct a Systematic Search for Evidence
• Searching the crime scene
depends on locale and size
of area as well as victims
and suspects
• Lead investigator will
subdivide the scene into
segments a search each
segment individually or the
search may start at some
outer point and gradually
move toward the center of
the scene in a circular
Conduct a Systematic Search for Evidence
• Areas searched must include all probable points of entry and exit
• Search for evidence will depend on type of crime:
– Homicide – Burglary – Vehicular – Kidnapping
• Physical evidence can be anything from massive objects to microscopic traces • Some objects may only be traceable in
laboratory settings therefore the
collection of possible carriers of trace evidence is important
– Minute traces of blood on clothing – Hair or fibers in vacuum sweepings
Conduct a Systematic Search
• The search for evidence continues in the autopsy of a deceased victim • Medical examiner will determine
cause and manner of death and will retain tissues and organs for toxicological and pathological testing
• The following should be collected and sent to the forensic lab:
1. Victim’s clothing
2. Fingernail scrapings 3. Head and pubic hair 4. Blood
5. Vaginal, anal and oral swabs (in sex related crimes)
6. Recovered bullets from the body 7. Hand swabs from shooting victims
Collect and Package Physical Evidence
• Physical evidence must be handled and processed in a way that prevents any change from the crime scene and the time it is received by the crime laboratory
• Changes arise through contamination, breakage,
evaporation, accidental scratching or bending, or loss through improper or careless packaging
•Whenever possible, evidence should be submitted to the lab intact; blood, hairs, fibers, soil particles should not be removed from articles
•Each different item or similar items collected at different locations must be placed in separate containers to prevent damage and
Examples of packaging containers and techniques:
• Plastic pill bottles for hairs, glass, fibers, and other types of small evidence
• Manila envelopes or screw-top glass vials for trace evidence (never ordinary
envelopes because of possible leaking) • To avoid accumulation of moisture and
mold, bloodstained materials should be packaged in manila envelopes or paper bags
• Clothing should be air dried and placed in paper bags to allow air flow
• Charred debris should be sealed in an airtight container to prevent evaporation • See Appendix I for proper collection and
Maintain Chain of Custody
• Chain of custody – continuity of possession must be established whenever evidence is presented in court
• Standard procedures include
– Recording the location of the evidence
– Marking it for id (collector’s initials and date)
– Properly completing evidence submission forms for lab analysis
– Accounting for every person that handles or examines the evidence.
Obtain Standard/Reference Sample
• Examination often requires comparison with a known standard or reference sample
– Hit and Run might require paint sample from car to compare to paint at scene
– Bloodstained evidence must be compared to blood samples or buccal swaps from all people at the crime scene
• Evidence may also be compared to substrate
controls – materials adjacent to or close to areas
where the evidence has been deposited
– If a burned area is suspected to be covered in gasoline, it should be compared to a similar area not suspected – Bloodstains on garments should be compared to area
Submit Evidence to the Laboratory
• Evidence is submitted by personal delivery or mail shipment depending on the location of the lab
• Evidence submission forms should be completed which provides a brief history of the case, the evidence submitted, and the type of analysis that should be preformed
• Analyst not strictly bound to specific test requested if new evidence is found or to search for trace evidence
Crime-Scene Safety
• Because of the presence of
biological substances with unknown pathogens, care should be taken to avoid contamination and infection • Guidelines set by the International
Association for Identification Safety Committee include:
– Wear protective gloves, shoe covers, liquid repellent coveralls – Mask/respirators, goggles, or face
shields
– Evidence possibly containing body fluids should be labeled as
Legal Considerations at the Crime Scene
• The removal of any
evidence from a person or from the scene of crime
must be done in conformity with the Fourth Amendment – the right against
unreasonable searches • There are cases when
police can justify a search without warrant
Other Forensic Science
Services
• Forensic Pathology
– The investigation of sudden, unnatural, unexplained, or violent deaths.
– Typically performed by coroners or medical examiners
– Primary role is to determine the cause of death; if the cause cannot be found through observation, an
autopsy is performed
• Cause of death can be classified into five categories:
Other Forensic Science
Services
• Forensic Pathology
– A medical examiner can often estimate the time of death by evaluating the stage of decomposition:
– Rigor mortis- immediately following death, when the body relaxes and then becomes rigid without the shortening of the muscles. Usually
occurs within the first 24 hours and disappears within 36 hours.
– Livor mortis – when the human heart stops pumping and the blood begins to settle in the parts of the body closest to the ground. The skin will appear as dark blue or purple in theses areas. Begins immediately after death and continues for up to 12 hours
– Algor mortis – process whereby the body temperature continually cools after death until it reaches room temperature; depending on the environmental conditions, beginning about an hour after death, the body will lose heat at a rate of 1-1.5 degrees Fahrenheit per hour
Other Forensic Science
Services
• Forensic Pathology
– Algor mortis – process whereby the body temperature
continually cools after death until it reaches room temperature; depending on the environmental conditions, beginning about an hour after death, the body will lose heat at a rate of 1-1.5
degrees Fahrenheit per hour
– Potassium levels in ocular fluid (vitreous humor) – after death, cells within the inner surface of the eyeball release potassium into the vitreous humor. By analyzing the amount of potassium present at various intervals after death, the rate at which
potassium is released can be determined. This rate can be used to approximate the time of death.
Other Forensic Science
Services
• Forensic Anthropology
– The identification and examination of human skeleton remains
• Bones undergo an extremely slow breakdown process • Can provide several types of individual characteristics:
– Origin – Sex – Approximate age – Race – Skeletal injury – Facial reconstructions
Other Forensic Science
Services
• Forensic Entomology
– The study of insects and their relation to a criminal investigation
• Used to estimate time of death
• Insects will infect body once decomposition begins and lay eggs; the entomologist can identify the
specific insects present in the body and approximate how long a body has been left exposed by examining the stage of development of the larvae
Other Forensic Science
Services
• Forensic Psychiatry
– The relationship between human behavior and legal proceedings is examined.
• Civil cases – determine whether people are competent to make decisions about preparing wills, settling property, or refusing medical treatment
• Criminal cases – evaluate behavioral disorders and determine whether people are competent to stand trial
• Also examine behavioral patterns of criminals to help develop a criminal’s behavioral profile
Other Forensic Science
Services
• Forensic Odontology
– Identification through dental records
• Because of teeth enamel’s resilience, the teeth will outlast tissues and organs as decomposition begins
• Characteristics of teeth, their alignment, and the overall structure of the mouth provide evidence for identifying a specific person
• Bite marks on a victim can be analyzed and compared to suspect
Other Forensic Science
Services
• Forensic Engineering
– Concerns itself with accident reconstruction and causes and origins of fires and explosions
Legal Considerations
• Mincey v. Arizona
– Undercover police officer, attempting to buy drugs, forced entry into the apartment and was killed
– Without a search warrant, police searched the apartment for four days recovering
bullets, drugs, and paraphernalia.
– Evidence was submitted into trial but since it was illegally seized the court could not convict Mincey
Legal Considerations
• Michigan v. Tyler
– Loren Tyler and his business partner burned down leased property
– Fire officials and police officers searched the premises after the smoke cleared, then 4 days,7 days, and 25 days later to collect evidence
– Tyler and partner were convicted but it was overturned as searches were made without warrants (only initial evidence collected at first search was allowed)
