Physical evidence is useful (1) to determine how a crime was committed, (2) to connect a suspect with the crime or identify the criminal, or (3) to clear an innocent person. At all crime scenes the area will be taped off to ensure there is no destruction of evidence. Only law enforcement necessary will be allowed into the crime scene where they must assess the scene and then comb the area for evidence such as blood, bullet casings, weapons, fingerprints, etc. Also at this time, detectives will interview witnesses and sweep the area to see if anyone living nearby has information.