We present AutoCore, an automated crash reporting application that uses VANETs (Vehicular Ad hoc NETworks) to provide authenticated digital video and telemetry data. This data is recorded by vehicles either involved in or at the scene of a crash and can be used by investigators to reconstruct the events that lead up to the crash. To secure this application, we present a security infrastructure that extends the state of the art in VANET security. In particular, the contributions of this infrastructure include (a) the concept of Road-worthiness Certificates, (b) use of these certificates in a practical scheme for the distribution of cryptographic vehicle credentials issued by regional transportation authorities, (c) a decentralized scheme for conditionally anonymous, inter-vehicle communication, (d) efficient support for the roaming of vehicles between different transportation authority jurisdictions and (e) an evaluation of our security infrastructure using AutoCore.