Probably a daft question but why would he report it to the police when he found the bodies if he was involved in some dodgy way? I’d have thought he’d shit himself and ring his superiors to see if they can just dispose of the bodies somehow and hope there is no trace of them that can be linked back to them.
Perhaps an attempt at hiding in plain sight. Call it in and cry innocence at what you thought was just cargo.
You don't pick up a trailer from the docks and then drive around the corner to look inside though.