How is crime lab evidence analyzed?

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Crime scene investigators send evidence, including the victim’s body, to a crime lab for examination. Evidence is carefully packaged and handled to avoid contamination, assigned a unique identity number, and extensively photographed. The lab examines evidence for fingerprints, fibers, biological material, and weapons. The autopsy is crucial in determining the cause of death and identifying the victim. Analyzing evidence helps law enforcement track down criminals and can help convict defendants in court.

In the course of a complex homicide investigation, hundreds of pieces of evidence can be sent to a crime lab, including the victim’s body. Investigators on the scene err on the side of caution when it comes to sending evidence to the crime lab, to make sure nothing important is lost. The victim’s clothing, carpeting, any biological substance found on site, insects, a weapon, and anything unusual will be photographed on site, bagged, and sent to the lab for further inspection.

From the moment evidence is packaged, it remains in a controlled chain of custody to ensure it is not contaminated. When it arrives at the crime lab, a lab officer signs and locks it or immediately takes it to a workbench for examination. All those handling the tests wear gloves and often also protective shields on clothing to further reduce the risk of contamination.

All evidence entering a crime lab is assigned a unique identity number and extensively photographed before being examined. The initial examination of the tests is usually combined with a dictated or written description that enters the records associated with those tests. Next, the evidence is dusted or smoked for fingerprints, before it can be consumed via manipulation. If fingerprints are found, they are lifted and set aside for cross-matching.

After fingerprinting, the evidence is examined for traces of fibers or biological material such as hair and blood. This evidence, in turn, will be carefully removed, bagged and numbered for detailed analysis. The fibers will be examined and photographed, as they can provide valuable clues; if at some point a victim was placed in the trunk of a car, for example, the fibers on her clothing could be used to determine the make of the car. Biological evidence is tested for DNA so it can potentially be matched to a criminal or person of interest who was at the crime scene.

The weapons found on the spot are also carefully examined. If the weapon was a handgun, ballistics tests will be done to determine when it was fired and to obtain clean bullet samples from the weapon that could be compared to bullets at the crime scene, to match the weapon with the murder. Knives and other tools are thoroughly tested for traces of biological material, and their shapes are photographed and described so that they can be matched to the victim’s wounds. If the firearm has a serial number or unique identifier, it will be entered into a database to see if any information about the firearm’s last recorded owner can be found.

The victim is taken to an autopsy room at the crime lab to be examined by a forensic pathologist, who may find evidence on the body such as fibers, biological material, and bullets that are sent back to the lab. The autopsy is a very important part of the examination, because it will determine the precise cause of death and also provide clues as to the time of death. The coroner will also be able to tell if the body was moved and identify the victim, if her identity has not already been established.
Analyzing evidence in a crime lab helps law enforcement track down criminals. Once someone has been arrested and formally charged, this evidence can also help convict the defendant in court if he is guilty. Once the evidence has been reviewed by the crime lab and shown in court, the jury decides whether it is convincing enough to merit a conviction or not.




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