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How Crime Scene Investigation Works

Finding Crime Evidence

Forensic specialists of the German police secure the crime scene
Forensic specialists of the German police secure the crime scene after a deadly knife attack on May 10, 2016, in Grafing, Bavaria. Johannes Simon/Getty Images


­The goal of the evidence-collection stage is to fin­d, collect and preserve all physical evidence that might serve to recreate the crime and identify the perpetrator in a manner that will stand up in court. Evidence can come in any form. Some typical kinds of evidence a CSI might find at a crime scene include:

  • Trace evidence (gunshot residue, paint residue, broken glass, unknown chemicals, drugs)
  • Impressions (fingerprints, footwear, tool marks)
  • Body fluids (blood, semen, saliva, vomit)
  • Hair and fibers
  • Weapons and firearms evidence (knives, guns, bullet holes, cartridge casings)
  • Questioned documents (diaries, suicide note, phone books; also includes electronic documents like answering machines and caller ID units)

With theories of the crime in mind, CSIs begin the systematic search for incriminating evidence, taking meticulous notes along the way. If there is a dead body at the scene, the search probably starts there.

Examining the Body

A CSI might collect evidence from the body at the crime scene or he might wait until the body arrives at the morgue. In either case, the CSI does at least a visual examination of the body and surrounding area at the scene, taking pictures and detailed notes.

Before moving the body, the CSI makes note of details including:

  • Are there any stains or marks on the clothing?
  • Is the clothing bunched up in particular direction? If so, this could indicate dragging.
  • Are there any bruises, cuts or marks on body? Any defense wounds? Any injuries indicating, consistent with or inconsistent with the preliminary cause of death?
  • Is there anything obviously missing? Is there a tan mark where a watch or ring should be?
  • If blood is present in large amounts, does the direction of flow follow the laws of gravity? If not, the body may have been moved.
  • If no blood is present in the area surrounding the body, is this consistent with the preliminary cause of death? If not, the body may have been moved.
  • Are there any bodily fluids present beside blood?
  • Is there any insect activity on the body? If so, the CSI may call in a forensic entomologist to analyze the activity for clues as to how long the person has been dead.

After moving the body, he performs the same examination of the other side of the victim. At this point, he may also take the body temperature and the ambient room temperature to assist in determining an estimated time of death (although most forensic scientists say that time of death determinations are extremely unreliable -- the human body is unpredictable and there are too many variables involved). He will also take fingerprints of the deceased either at the scene or at the ME's office.

Once the CSI is done documenting the conditions of body and the immediately surrounding area, technicians wrap the body in a white cloth and put paper bags over the hands and feet for transportation to the morgue for an autopsy. These precautions are for the purpose of preserving any trace evidence on the victim. A CSI will usually attend the autopsy and take additional ­pictures or video footage and collect additional evidence, especially tissue samples from major organs, for analysis at the crime lab.

Examining the Scene

There are several search patterns available for a CSI to choose from to assure complete coverage and the most efficient use of resources.

The inward spiral search: The CSI starts at the perimeter of the scene and works toward the center. Spiral patterns are a good method to use when there is only one CSI at the scene.

Inward spiral search pattern
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The outward spiral search: The CSI starts at the center of scene (or at the body) and works outward.

Outward spiral search pattern for crime scene investigation
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The parallel search: All of the members of the CSI team form a line. They walk in a straight line, at the same speed, from one end of crime scene to the other.

Parallel search pattern in crime scene investigation
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The grid search: A grid search is simply two parallel searches, offset by 90 degrees, performed one after the other.

Grid search in a crime scene investigation
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The zone search: In a zone search, the CSI in charge divides the crime scene into sectors, and each team member takes one sector. Team members may then switch sectors and search again to ensure complete coverage.

Zone search in crime scene investigation
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While searching the scene, a CSI is looking for details including:

  • Are the doors and windows locked or unlocked? Open or shut? Are there signs of forced entry, such as tool marks or broken locks?
  • Is the house in good order? If not, does it look like there was a struggle or was the victim just messy?
  • Is there mail lying around? Has it been opened?
  • Is the kitchen in good order? Is there any partially eaten food? Is the table set? If so, for how many people?
  • Are there signs of a party, such as empty glasses or bottles or full ashtrays?
  • If there are full ashtrays, what brands of cigarettes are present? Are there any lipstick or teeth marks on the butts?
  • Is there anything that seems out of place? A glass with lipstick marks in a man's apartment, or the toilet seat up in a woman's apartment? Is there a couch blocking a doorway?
  • Is there trash in the trash cans? Is there anything out of the ordinary in the trash? Is the trash in the right chronological order according to dates on mail and other papers? If not, someone might have been looking for something in the victim's trash.
  • Do the clocks show the right time?
  • Are the bathroom towels wet? Are the bathroom towels missing? Are there any signs of a cleanup?
  • If the crime is a shooting, how many shots were fired? The CSI will try to locate the gun, each bullet, each shell casing and each bullet hole.
  • If the crime is a stabbing, is a knife obviously missing from victim's kitchen? If so, the crime may not have been premeditated.
  • Are there any shoe prints on tile, wood or linoleum floors or in the area immediately outside the building?
  • Are there any tire marks in the driveway or in the area around the building?
  • Is there any blood splatter on floors, walls or ceilings?

­The actual collection of physical evidence is a slow process. Each time the CSI collects an item, he must immediately preserve it, tag it and log it for the crime scene record. Different types of evidence may be collected either at the scene or in lab depending on conditions and resources. Mr. Clayton, for instance, never develops latent fingerprints at the scene. He always sends fingerprints to the lab for development in a controlled environment. In the next section, we'll talk about collection methods for specific types of evidence.