A State Bureau of Investigation (SBI) is a state-level detective agency in the United States. They are plainclothes agencies which usually investigate both criminal and civil cases involving the state and/or multiple jurisdictions. They also provide technical support to local agencies in the form of laboratory or record services.
An SBI is a state's equivalent to the Federal Bureau of Investigation. The SBIs investigate all manner of cases assigned to them by their state's laws and usually report to their state's attorney general, or in some cases to their state's governor.
SBIs can also exist either independently or within a Department of Public Safety (which is an umbrella agency coordinating and/or controlling the various state level law enforcement agencies) or a state police force (which is a general law enforcement agency).