Not because he was actually up for parole (it was denied). Not because he doesn't show any remorse (he does). But because it just reminds us of how incredibly senseless Lennon's killing was.
Chapman only did it to get attention. How sick is that? And even though we've been told for 30 years that he called out "Mr. Lennon" before he shot him, he actually didn't say anything at all. He just shot shot him in the back. In the back. For no reason at all.
