Ted is dead. Think about it - we saw him fall and seriously injure himself (he knocked himself unconscious at the very least). Once that happened, he was as good as dead. He is living alone in an empty house and the only witnesses to his accident were two criminals who weren't supposed to be there. Clearly, they were…

Even if they were able to recover the gun from the aftermath of that fire, I doubt there would be enough left of those bodies to determine the cause of death at all, much less that they were killed by a specific gun. Also, I would imagine there is more than one guy who can sell you a pistol with the serial number…