Yes, like perhaps stolen or borrowed for the afternoon or simply registered to more than one owner (husband/wife; father/son etc...) or registered as a company vehicle.
I think it is very relevant that when Carter 'got down to business' with the presser (after thanking the community for their support) the first thing he said was: 'we are seeking the identity of the driver of a vehicle parked at the old CPS building...'. This is the key piece of evidence they need, IMO, to nail their suspect. LE knows the make/model and maybe even the plate # of the vehicle that was there, they just don't know or can't prove who was driving it without a witness.