I think there's more to the story about a disagreement Billy Wagner had with Chris Sr and Kenneth. Billy has long been a violent **** who was known to bully people in the community. He had a violent conflict with Chris Sr not long before the murders. He was as motivated as the rest, don't let him fool you.
JMO
ETA: WS censored the name I used to refer to Billy, but I promise it wasn't a curse word.

That said, I'm going to leave it like that because now it looks like it was.

It's a word that rhymes with "bug".
ETA #2: Does anyone else think Billy's extra tight security might have to do with LE hearing him say things in jail or in his phone calls? He's been in jail quite a while, they probably know him pretty well by now.