Senior Inspectors locate witnesses, interview witnesses and suspects, visit crime scenes, gather and preserve evidence, take still and video photographs, serve subpoenas and other legal papers, request complaints, appear as witnesses and testify at inquests, court proceedings, and Grand Jury sessions. Experience: Three years of full-time experience as an investigator or detective in a public law enforcement agency investigating felony crimes such as homicides, burglary, narcotics, sexual assault, and domestic violence, or three years of experience as District Attorney Inspector-Welfare Fraud in Contra Costa County employment.