How do we handle a case where a mass shooter keep shooting people? You get a police to arrest the aggressor first and get them to court. We can simply get a p

How do we handle a case where a mass shooter keep shooting people? You get a police to arrest the aggressor first and get them to court. We can simply get a police to issue an arrest, ban him from social network, get him to court later. I don't think this problem is particularly hard. Not sure why a lot of people seem to think that this is impossible to resolve through legal system. Trump is leading the riot/coup. He should be arrested immediately, no? (In some countries, that's a death sentence.) It's either (1) Trump isn't really leading the riot/coup or (2) leading the riot/coup isn't unlawful. I'm confused on this contradiction of reality. Somebody is lying here.