lockin
if it was so easy for sir john to lock himself in during the full moon why did he need singh to do it for all these years?
"I think I liked it better when I thought Sylar ate brains."
Remember when Laurence was in the billiard room (or whatever) with Gwen, and he could hear her heartbeat and there was the threat of his baser impluses taking over? I think that was meant to imply that once a werewolf, a man couldn't return to being fully in control, even between moons.
So it's likely that Sir John needed persuasion from Singh to do the right thing and lock himself in all those years. When he locked himself in without Singh's assistance it was because he had an ulterior motive that overrode his baser instinct, and that was to set his son up for the murders he knew were soon to come.
Time of your life, huh, kid?