My Version of the Ending
I won't reveal the real ending and spoil it for others, but my own version would have been that AFTER amputating his genitals (as a "souvenir,") I would have doused him and the entire room with gasoline, then tossed a match.
Later on, I would have tracked down his wife and kids, doing to them what Michael did to his own victims.
His entire DNA strand must be eliminated, not just him.