Cop has only a measly 5HP
(twitter.com)
Humans hate captivity, no matter how comfortable. We need more, a purpose to be whole. He's been given an enemy to fight against that 90% of the world is ok with killing (Aryans, Whites, whatever you want to call us). So, he probably sat around getting fat and high and angry in his box he calls a home until he thought up some way to lash out.