That was the problem. As you know, the "agitators" weren't burning buildings, killing police, or rioting. They were just protesting. Trump's secret police initially weren't actually able to find any criminals, but they did grab some people off the street and hold them without charges. Apparently, they were recruited ICE agents, and so not very useful for actual law enforcement.
More recently, they seem to have actually started to enforce the law...
On Monday night, there were seven arrests, said Federal Protective Service Deputy Director of Operations Richard Cline. Two of the arrests involved assault on a federal law enforcement officer and the other five were misdemeanor charges.
"Assaulting police" is a common charge, one of the least effective in terms of getting a conviction. It's usually something tossed in when there's nothing else that can be applied.
But it may be that the massive presence of these unidentified troops may have actually arrested five vandals.
The local police were a lot more effective than that. But then, they are police.