There is never, ever, ever any possible excuse for kidnapping people without due process. Ever, ever. Because there's no way to prove that they were violent rioters. They just as well could have been total innocents, and you'd have no way to know.
Proving whether that person participated in the riot is a matter for the courts, all that's needed for an arrest is reasonable suspicion.
I don't know if you are a native speaker, but the word kidnap might not be the one you should be using. "Kidnap" has strong connotations, and while sime people will happily use that property of the word to create feelings I don't think it is appropriate here.
kidnap: abduct (someone) and hold them captive, typically to obtain a ransom.
There's a lot to be said about police, federal agents, TSA etc, but lets keep this serious.