IDK, a potpourri of Charles Manson, Jeffrey Dahmer, and Hannibal Lecter comes to mind. Also Narcissistic Personality Disorder and Antisocial Personality Disorder, and neither are favorable as far as rehabilitation. Could be other things involved as he seems quite delusional, but that can be a component in the two disorders. Maybe he is Schizophrenic or Bipolar, but I just think there's more going on than that. Most Schizo's and Bipolars don't do what he did, in fact probably very few.
Something else comes to mind, that old movie The Bad Seed starring Patty McCormack (i.e., Sociopathic / APD). Only in LM's case, he didn't have a mother to do him in, so therefore got older and had the opportunity to learn and do more vile things; plus little Patty didn't have the WWW or violent video games, etc. to help nurture her talent.