Criminal Justice Versus a Sitting Attorney General

I have a question; maybe one of you understands how this works.

When the attorney general of the U.S. is a lawbreaker, what part of law enforcement deals with him? Capitol Police? I’m asking because I don’t know the answer.

If the House decides to subpoena Barr or hold him in contempt of Congress, is there someone who could actually arrest him? The Sargeant-in Arms of the House is supposed to be the person to arrest someone in contempt of Congress, but what if Barr decides he doesn’t peacefully want to be arrested? Barr is, after all, the head of all federal law enforcement.  I’m not sure how arresting him would work.

The famous example of John Mitchell doesn’t provide an answer, because Mitchell wasn’t indicted while in the office of attorney general.. Mitchell resigned in 1972 to manage Richard Nixon’s re-election campaign. He wasn’t indicted until 1974, and he began his prison term in 1977.