I don't think we do know who was behind this, and if you're saying "let's not jump to conclusions", then how about not making snarky comments implying just that.
The attorney for Brent and Grant was reported in the news media as saying that, as far as he knew, his clients were in San Diego the night of the murder. That would make it very difficult for them to simultaneously be 2,000 miles away. My understanding from the news articles is that the information they have relates to having spoken to Bryan on the phone and Bryan mentioning that someone was coming over for a photo shoot. That's a far cry from being in Dallas, PA at the time of the murder.
Look at the situation. The lawsuit was ugly, a lot of nasty things were said by both sides. So obviously Grant and Brent (Sean) would be on the suspect list. ANYONE with an ounce of sense would want competent counsel before saying anything to the police in a situation like this, whether or not they were innocent. You don't have to watch too many episodes of "Law and Order" to figure that out.
Additionally, the lawsuit had been settled. It would have made a lot more sense to take Bryan out before the suit was settled than to do so after, when the settlement (which apparently had a significant portion of future earnings for Sean's site going to Cobra) was signed and would be binding even after Bryan's death.
Is it possible that Grant and/or Sean hired somebody to do this? Sure. Is there any evidence whatsoever that any of us in the GWW community have indicating this? No.
As such, reckless comments like "I'm guessing we probably know who did this" are irresponsible. There's enough drama in the situation already. Let's not feed the fire.