Evidence found at the scene of a crime must eventually be presented and questioned in the courtroom. For the evidence to be of use in a trial, it must make the journey from crime scene to court in a validated and secure manner so that all involved can be assured that it has not been contaminated and that the evidence is relevant to the crime investigation. In order to insure validity, investigators must follow a routine commonly known as the chain of custody when it comes to collecting and handling evidence.
The first person to collect an item of evidence, be it a bloodstain or a bullet, will sign their initials and date either on the item itself or on its packaging. Clearly, marking an item ensures there is no ambiguity, as packaging could be separated from the evidence itself. However, some types of evidence, such as bullets, may be altered if marked and, of course, it is not possible to mark evidence like bloodstains or fingerprints directly.
Evidence usually goes from the crime scene to the forensic laboratory for examination where the receiving officer signs the evidence package and dates it. Everyone who handles the evidence does likewise until the analysis is complete. At this stage, the evidence will be given to the police for storage until its presentation in court. The receiving police officer will sign for the evidence and it will be stored in a secure area to minimize the risk of interference or loss.
When the case is presented in court, the prosecuting lawyer takes over custody of the evidence and signs to that effect. If the chain of custody procedure is handled correctly, the case can proceed with all involved being aware of the precise journey the evidence took from crime scene to the court. This allows evidence to be admitted in court, and witnesses to have the assurance that the item of evidence was indeed present at the scene of the crime and testify accordingly. The judge and jury are then able to use the evidence, along with witness statements and other information, to guide their decision-making process.
SEE ALSO Crime scene investigation; Cross contamination.
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