I believe I've seen the one you speak of. If it's the same one I've seen, I do not believe for a second, it is the drawing of "sketch artist". However, based on that post, about that vehicle, and that night of the murders, I've a feeling that the W's spread the love around, in attempting to throw off suspicion. It's also quite possible that JM's vehicle was not the only that had a tracker on it at some point. JM just happened to find his, and by removing it, could have made it appear that he too had a "bug buster", hence his arrest for tampering, and visit to the Grand Jury.