The police investigation is the series of steps that law enforcement officers take to establish the facts and uncover the truth in a criminal case. Police investigations can close cases and prevent new crimes from occurring. Police agencies use a variety of tools to carry out a police investigation, including interviews and interrogations, physical evidence and electronic evidence like cell phone data. NIJ supports research to improve investigative techniques, crime mapping, evidence reliability and to enhance training in investigative procedures.
When police arrive at a crime scene they will start collecting evidence. They will take notes about the scene and record what they find, creating a chain of custody to ensure that the evidence is not tampered with or destroyed. This includes physical items such as blood, fingerprints, hair and saliva and electronic information like cell phones, online searches and communications. Police will also take photographs and make detailed observations about the surrounding area.
Police will then interview any witnesses, ensuring that they can capture each witness’s individual recollection of events. They will also interview any known suspects, if they can be located. Depending on the crime, investigators may want to examine injuries to victims and take photos of any marks or scars that occurred. If necessary, they will have medical professionals engaged to conduct a medical exam and photograph any injuries.
Detectives will also investigate potential gang activity and methods of recruitment in their respective areas. Gang squads work closely with precinct detectives to identify and dismantle gangs throughout the borough, as well as to coordinate with local, state, and federal authorities on joint prosecutions.
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