Explain the 'chain of custody' principle, and describe the critical steps required to maintain it for evidentiary purposes.

The 'chain of custody' is a crucial principle in evidence handling, ensuring that evidence presented in court is authentic and has not been altered or tampered with. It refers to the documented chronological history of who had possession of a piece of evidence, when, and what they did with it, from the moment it was collected until it is presented in court. Maintaining a proper chain of custody is essential for establishing the admissibility of evidence; if the chain is broken, the evidence may be deemed inadmissible. Several critical steps are required to maintain a chain of custody. First, the evidence must be properly identified and labeled at the time of collection. The label should include the date, time, location of collection, a description of the evidence, and the initials of the person collecting it. Second, the evidence must be properly packaged and sealed to prevent contamination or tampering. The packaging should be appropriate for the type of evidence and should be sealed in a way that makes it obvious if the seal has been broken. Third, a custody log or form should be created to document the transfer of the evidence from one person to another. Each time the evidence changes hands, the date, time, and name of the person relinquishing and receiving the evidence should be recorded on the form, along with a brief description of what was done with the evidence. Fourth, the evidence should be stored in a secure location with limited access. The storage location should be controlled to prevent unauthorized access or tampering. Fifth, any analysis or testing performed on the evidence should be documented. This includes recording the date, time, and nature of the analysis, as well as the name of the person performing the analysis. For example, if a blood sample is collected at a crime scene, the person collecting the sample would label it, package it in a sealed container, and record the collection information on a custody form. When the sample is transferred to the lab, the custody form would be updated to show who relinquished the sample, who received it, and the date and time of the transfer. The lab technician would then record any analysis performed on the sample and the date and time of the analysis. This process would continue until the evidence is presented in court, ensuring that a complete and unbroken chain of custody is maintained.