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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.

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The Crime Scene

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physical evidence
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
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
Recording the Crime Scene
  • 3 methods of crime-scene recording: photography, sketches, & notes
  • Ideally all 3 should be used
  • 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
  • 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.
  • 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.,


Finished-sketch diagram of a crime scene. Courtesy Sirchie Finger Print Laboratories, Inc., Youngsville, N.C.,

  • 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
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
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.
collect physical evidence
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 evidence16
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 evidence17
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 cross-contamination.
autopsy room
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:
    • 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
Tools for Evidence Collection
  • 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.
chain of custody
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
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 samples23
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
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
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
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
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

other specialties29
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
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.