the Tale of Metal Mouth

Ever wonder about those roof noises?

About a decade ago, a boy was insulted almost everyday in high school because of his braces almost. He couldn't simply remove them, so teachers hardly helped. In the classroom, in the hallway, in the gym locker...his braces remained.
One night in his room he even smashed the mirror after smiling, then used the shards to attempt suicide by slitting his wrists. He paused, however, and thought that people get braces all the time...so it wasn't he who should be blamed, but them. First he murdered his parents for agreeing with paying for the braces, and lying to him that it looked fine. Using his father's doctoral supplies, he injected acid directly into their flesh. The following days he murdered any who insulted him, one by one.
Of course, that is only what we suppose his history is...we call him Metal Mouth because of what witnesses have reported most recently. He maneuvers via rooftops wearing a black cape, where he peers through the windows across the street, deciding who to kill next... He smiles at any who spot him, with his gleaming braces still on, which have deranged his teeth now. Probably because he never cared to get them tightened or cleaned ever since his parents...
During the night he makes his way onto the next victim's roof, then intrudes to inject more acid. Open windows make easy entry, and for some reason dolls attract him (based on patterns studied by the police)..
What infuriates him is when he's going in for the kill, and the victim gets up suddenly, whether it be for a drink or piss. The death will be more brutal then, as a result of his rage.
So why does he kill? Well, let's just say that a killer becomes more insane with every kill.
And what does he eat?

You!!!