The National Insurance Crime Bureau (NICB) is a non-profit organization dedicated to fighting insurance fraud and crime. They work with the insurance industry and law enforcement on fraud and theft investigations. They also advocate legislation related to insurance fraud and vehicle theft.
The NICB offers a free service to the public to allow VIN searches of their database to determine if a vehicle has been reported as stolen or reported as salvage.
You can find the free report here: https://www.nicb.org/theft_and_fraud_awareness/vincheck