The police investigation is a process by which the facts about a crime are gathered in order to determine whether an offence has been committed. It involves impartially following all reasonable lines of enquiry and gathering material that points both towards and away from a suspect and that will ultimately support prosecution, an out-of-court disposal or community resolution.
Police and investigators may use many different techniques to gather evidence, including CCTV, blood analysis, fingerprinting, voiceprinting, photography, document examination and the crime laboratory. Modern forensics technologies such as DNA examination and digital forensic analysis are increasingly important tools in solving crimes. Investigators are also skilled in identifying and interpreting witness testimony, interviewing suspects and witnesses, arranging court dates for preliminary hearings and grand jury sessions, and preparing cases for trial.
A key element of police investigation is ensuring that the right amount of evidence is collected, handled and stored to maintain the integrity of the evidence. For example, improper storage of biological samples could lead to mold growth or cross-contamination. Investigators also need to be creative when finding ways to get reluctant witnesses to give a statement and to overcome other challenges such as insufficient forensic results.
Often, detectives and police officers need to obtain warrants to search a person’s property or make an arrest, which requires them to have probable cause. They must ensure that they do not violate a suspect’s rights and that all statements made are voluntary. This is particularly crucial for investigations involving child abuse, hate related incidents and domestic violence.