So that was a bit of a surprise. I was expecting Chase to be Vigilante, not Prometheus.
How is the Green Arrow going to get out of being a murder suspect this time? Maybe, like the "Arrow" before him, he'll "die" and be replaced by a new archer vigilante with a different colour. Oliver better start finding a new colour for his costume.
But if they don't take that route (because it's been done before and would stretch credibility for anyone in Star City to believe that again), what if Billy Malone is actually not dead but working with Prometheus all along? That would exonerate Green Arrow, because he hasn't killed anyone at all. And if he was Prometheus part of the time, it could explain how Chase might seem to be in two places at once (although I can't remember if we ever saw him when we saw Prometheus).
Wasn't Chase the one who ordered the cover up of Billy's death and Oliver merely approved it? So in fact, Chase might be the one who has also managed to arrange for a fake death report.
And if Billy isn't dead, maybe he's Vigilante. When did Vigilante first appear this season?
If Billy turns out to be Adrian's brother, then maybe they have a vendetta against each other if they're not in league with each other. Or maybe Billy now has a vendetta against him because Adrian tried to have him killed by GA.
The only other way for Green Arrow to be exonerated is to somehow prove that Prometheus was behind the murder and tricked Oliver. But how would anyone prove that? Were there any security cameras anywhere? Maybe they'll make it that Felicity is now so good at hacking that she can hack security footage where there was none and where cameras didn't even exist.