Precrime Arrest: Well, while this sort of thing is easy enough to do with behavioral analysis software and ubiquitous computing and AI monitoring and all the other appurtenances of Citizen Oversight, obviously you can’t arrest people before the crime, having a great and tremendous respect for free will and all. That would be very bad form indeed. (I mean, if they were certain to commit the crime, that would be fine: under Imperial notions of the legal causality of intent, that’s why you can arraign someone for murder even if they were stopped before proceeding, but if they haven’t committed to their mens rea yet, it’s not a crime even if it was very likely to be, and free-will choices in critical moments are awkward that way.)
But there’s ain’t no rule saying you can’t quietly park a UAV with a stunner, say, in the air over people who are very likely to be about to commit crimes just in case, or quietly take other precautionary measures. If it turns out they don’t – well, no harm, no foul. That’s not an accusation, it’s just probability-based policing.