When police investigate a crime, they gather information and evidence to build a case that will lead to criminal charges. Investigators use a variety of tools to conduct their investigation, including interviews and interrogations, physical and chemical tests, and other methods of collecting data and evidence. NIJ supports investigative technology and training to improve the effectiveness of law enforcement agencies.
A criminal investigation can begin with a call about a crime or even a sighting of someone who is suspected of committing a crime. First-responding officers will then complete a primary assessment of the scene to locate any potential threats. Officers will also start a log to create a record of everyone who enters and exits the area, so that the integrity of the crime scene is preserved.
After the crime scene is secured, police will interview witnesses and suspects. Interviewing involves a series of questions designed to gather detailed, accurate information about the incident. Often, multiple witnesses will describe the same events differently, and police interview witnesses separately to ensure they have each witness’s individual recollection. Detectives may also interview people who have a relationship to the suspect, such as co-workers or friends. Depending on the case, the police may conduct surveillance or check public records to identify suspects.
Interviews are one of the most important aspects of a police investigation. However, they can be a source of controversy. A false confession can occur when a person admits to a crime they did not commit, usually because of coercive interrogation techniques like prolonged questioning and threats. The police interview process has become a focus of reform due to high-profile cases that have raised concerns about the accuracy and fairness of questioning tactics.