The SIU is a civilian law enforcement agency, independent of the police, that investigates circumstances involving police and civilians which have resulted in serious injury, including sexual assault, or death. Part VII of the Police Services Act creates the SIU and defines its powers.

Independence
The SIU is independent of any police service. The Unit reports to the Attorney General, however the SIU's investigations and decisions are also independent of the government. The Director of the SIU is empowered under the Police Services Act with causing criminal charges to be laid against police officers where warranted on the basis of the evidence gathered during an investigation.

Civilian Oversight of Policing
Although unique in model, Ontario's SIU is part of a worldwide movement on the part of governments aimed at enhancing mechanisms of police accountability. The SIU's motto: Independent Investigations, Community Confidence.