You're right, but iirc, he was the one person who wasn't drinking, who was in bed asleep fairly early, who didn't see a dangling foot, who wasn't tink-tinking on his phone ... as lax about home security as he may have been, I think he seems fairly unlikely to have been involved in whatever happened that night based on the accounts that have been given so far, assuming they're true. Other family members may still be pinging LE's radar, though, for sure.
Regardless, I am definitely impressed by their work on this case. It's been heartbreaking for them, by all accounts.