“Yeah, the guy who used to own the place was taken in for questioning, but they had to let him go ‘cause there wasn’t any incriminating evidence against ‘im. Smug bastard got away with it, I’ve always said. God knows what those beetles are always clicking about at these odd hours. Death-watches, I hear that’s what they’re called.”

With how the body was eaten, I'd put this on 'artistic_license:_forensic' pool if there's one. For one thing, if they had managed to eat the whole torso part, the cockroach would definitely already eaten off the face, which comprised of softer tissue compared to the muscles outlining the ribcage and the back. Another one would be entry points: cockroaches always tries to eat things from inside-out, so the open mouth would be a perfect entry point for the cockroach to start eating the head part inside out, maybe bite through the soft esophagus to reach brain.