I’m not gonna pretend to be an expert on US law, but my understanding is that only the DoJ can prosecute Federal crimes (and AG Barr controls the DoJ), which must occur in a Federal court.

Since all of this would fall under Federal crimes instead of State - and thus outside their jurisdiction - I would have assumed that they wouldn’t have any ability to do much more than detain them until the time period runs out for pressing charges, and a google search would suggest that State LEO are only able to arrest someone for Federal crimes if specifically empowered to do so for that specific Federal crime.

Is that not the case? Sorry for the intrusion, I’m just curious and half asleep right now (non-American).