Your point by point list was good, but don't overplay your hand. I haven't seen any information that they were paid or mercenaries. Have you, or did you just make that up?
Do not underestimate the lure to these thugs of participating in a riot situation GRATIS. In all probability, they thought that coming for the evening would be entertainment. The opportunity to attack this scrawny 17 year old who was already on the ground was just going to be ever so fun, or so they thought.
On the other hand, if you have any proof they were paid, please share.
Dunno.
But two of ‘em were bused in. Sounds like organization, and a paycheck, to me.
If their sponsors can find funds for bail money, I would expect to be able to pay these people, too. It would be worse if they were living on the taxpayer’s dime.