Police investigations involve the search for and collection of evidence to support criminal trials. This evidence can come from a variety of sources, including physical objects and documents. Investigators will typically work with a crime laboratory to help them identify the source of the evidence through chemical or other methods.
Investigators will also need to preserve the evidence they collect. This involves storing it in the proper containers, such as paper bags to inhibit mold growth or anti-static bags for electronic samples. Failure to do this could lead to contaminated evidence, which would not be admissible in court.
In addition to collecting physical evidence, detectives will likely interview people who witnessed the crime or suspects. These interviews are often recorded and transcribed for later use in court. Officers and detectives will need to have a solid understanding of the psychology of interrogation to get useful information from suspects or witnesses. Some of the techniques they may use include the cognitive interview method and Reid technique.
Detectives may need to obtain warrants to search a person’s home, clothing or car to find evidence of a crime. They may also need to get a warrant to access someone’s social media accounts to find evidence of a crime or possible plans to commit one.
The police will also need to liaise with the public prosecution service (PPS) to decide what charges, if any, should be brought against a suspect. This will usually be based on the type of crime, the amount of evidence and whether there is enough evidence to prosecute.