In police terms, CI stands for Confidential Informant. A confidential informant is a secret source who, through a contact officer, supplies information on criminal activity to the police or law enforcement agent. The police often use confidential informants to identify and obtain evidence against persons involved in criminal activity. Confidential informants are usually criminals who cooperate with the police on an investigation. They can provide useful and credible information to a law enforcement agency regarding felonious criminal activities and from whom the agency expects or intends to obtain additional useful and credible information regarding such activities in the future.