A police investigation is the process that the police go through to identify suspects and build a case against them. The detectives use witness statements, physical evidence, and forensic investigations to determine whether or not there is enough information to charge someone with a crime. They may also check databases such as CODIS, the Combined DNA Index System and IBIS, and investigate leads from public tips or informants.
A key part of a police investigation is making sure that the officers involved are properly trained to observe and notice certain things, such as weapon positions, blood stains, footprints, fibers, fingerprints, or other clues left at a crime scene. Officers learn to note these details and document them in a report that is accessible to other police officers, investigators, and prosecutors. In some cases, they will also take photographs or ask to have the victim or witness examined by a doctor who can record any injuries.
Depending on the nature of the crime, investigators will also interview witnesses to get their statement about what they saw or heard. They will try to speak to anyone who has personal knowledge of the incident, which includes family members of alleged perpetrators. This is where things can start to get subjective, such as noting a person’s expression and how they responded, but that type of observation does help prosecutors build their case.
During an investigation, the police will work a case aggressively until they have exhausted all known lines of inquiry or there is no more useful information to be found. Once they have finished their investigation, they will pass the information to the Crown Prosecution Service, which decides whether or not it’s in the public interest to take a case to court.