She knew it was a legal arrest, but she wanted to arrest all 6 of them to make a big statement and calm the rioters. AND she wants some leverage to try and make some deals, imo. If she can have some wiggle room to let some off in exchange for damning info against the others she is in good shape. So she trumped up charges against a couple to take down the rest, imo.
Happens everyday by prosecutors. It sucks, but thats how the justice system works.