So he either "doesn't remember" (aka "quick, ignore the inconvenient truth!") and he's a liar, or he actually doesn't remember...in which case he's a psychopath. If you torment someone systematically for an extended period of time, and this doesn't leave a notable impact on your brain enough to be worth remembering - in other words, deliberately hurting someone just fades into the background noise of your life - something's wrong with you.