I'd have to say, if I'd witnessed this happening, I'd picked up the bluntest object I could find to see how far I could knock this guy's head into the next county. I mean, the guy was gnawing at another human's face! Sometimes it's not prudent to call the cops (we ridicule so much) while sitting by witnessing horror in the making.
I would have batted a 1000 on this guy's head.