The police investigation is the process of gathering and analysing evidence that will be used to prosecute a suspected criminal. The outcome of the police investigation may result in a prosecution in court, out-of-court disposal or community resolution. The investigative process requires a number of different procedures that are designed to ensure the quality of the evidence. These procedures are often referred to as the RTM: Response Transition Matrix.
Depending on the crime the first priority of an investigator is to take immediate action in order to protect life and safety. Once this is done the detective can move on to the next step of an investigation, which is to gather information on the case. This includes taking witness statements and conducting a site investigation.
The investigator will look at the scene of the crime, noting details such as weapon positions, blood stains, footprints and other clues. They will also have a crime lab examine samples, such as DNA and fingerprints. These tests will be run against known databases in an attempt to identify suspects (even if there is not enough other evidence at the scene of the crime). The investigator may also conduct interviews with witnesses. Usually they will interview witnesses separately, as this allows them to record each person’s unique recollection of events.
In some cases, an investigator will be required to search private property such as a home or car. The police must obey the law regarding when they can do this and must have probable cause in order to obtain a warrant or to enter without one. During the interrogation of suspects, investigators must also respect the rights of the accused. Any evidence obtained through inappropriate means or without probable cause can be repudiated in court.