I'm guessing the tape is our best bet since industrial type tape rolls (duct, packing, etc) can get pretty nasty and pick up a lot of stuff. It's probably the item most likely to preserve evidence, whether it's fingerprints or anything else. If he ever sat the roll of tape down in his vehicle outside of a bag, perhaps enough fiber or material from the floorboard or seat upholstery would've stuck to the side of the roll of tape to identify the specific make and model of his vehicle. With luck, maybe there's hair, fingerprints, or even skin cells. I know my tape rolls are pretty damn nasty on each side. Hopefully his was.