I think Mookie only came up with this "twist" today.

Well, first off, we DONT know that he hasnt mind controlled someone close by. Last second sleeper agent attacks are a fairly common trope in this sort of story. But, even if he doesnt do that, there is a good excuse. He doesnt want to take that risk. If any of the people there suddenly start acting even a little different, it could raise suspicions. Combine that with him needing the time and opportunity to cast his mind control, and its a dicey prospect. That being said, literally anyone who has been away from the crowd for more than a minute could be turned into the last second sleeper agent. Luna might be a sleeper, but then again, she is just so great that it would only cause one strip drama as she breaks through out of twu wub.
I'm doubting that Mookie could pull even that off. It would just go from:

Normal -> Murder