Can't keep this back any more and do not know if this was speculated in another place.

I think Vic was in on the killing of Sean. He is tortured by that guilt when we first meet him. He did not come clean on that point because, well what's the point. It becomes harder to break that silence and the lie of omission is stuck to. Now, he is really in a bind because he is back with the Colony. Ugh. And with Tanya and CJ. Double Ugh.