if they dumped the child seat down the road it was taken for a joyride imo, someone taking it to strip it at a unit would have not bothered removing the childseat.

Chances are it is local, take a trip out late evening would be my guess and see what turns up. But be careful, don't go chasing after them in your motor, as it aint their car so they will have no hesitation in raming you, leaving you with two smashed up motors.