I've been doing catch up on Arrow, basically watched all of Seasons 1 and 2 over the course of a week, and am on the 3rd episode of Season 3. After Sara's murder, I've been trying to ponder the who Sara's killer could be. I had a theory, but I decided to check out to see if there were ways you could mess with audio editing tools to clear up voice changers. Turns out someone had a similar idea, so I converted the episode copy I had into an audio file, and then messed with the pitch (upped it between 55 and 65%), and unless they're pulling a fast one, that sounds like Thea's voice (at the very least, it's definitely female). Now, maybe over the next three episodes something will torpedo that, but it actually fits my theory so far. The idea being that Sara wouldn't have automatically reacted to Thea with surprise or alarm, and the three arrow grouping is Malcolm's signature for killing a target, something he could have easily passed on to his daughter.
I think Ollie's little sister has gone over to the dark side.