Complex sentence: Commissioner Anthony W. Batts reported that, contrary to department policy, the officers did not buckle him inside the van when being transported to the police station--a report supported by a medical investigation which found that Gray had sustained the injuries while in transport.
Split into simpler sentences: Commissioner Anthony W. Batts reported that, contrary to department policy, the officers did not secure him inside the van when being transported to the police station. The medical investigation found that Gray had sustained the injuries while in transport.