Thank you. I understood that. What I was trying to find out was whether he was rearrested on new charges when he was put in.
You asked about a false arrest. For your son to be a victim of a false arrest and a wrongful detention, the marshals would have had to be exceeding their authority by bringing him in and having him incarcerated without probable cause to do so. If there was no probable cause, his subsequent detention was unlawful.
Probable cause is a reasonable belief that criminal activity may be afoot and that a particular person may have been involved in it. With probable cause -- doesn't take a lot of evidence -- the state can get a warrant, make an arrest, file charges and secure an indictment. If the marshals really did have reason to believe that your son was involved in a criminal activity or in violation of his original bond conditions, they the arrest wasn't wrongful. If they had no real basis to pick him up, then he would have a case.
False arrest/wrongful arrest is a civil and not a criminal matter and requires a civil rights lawyer or a general civil litigator (trial lawyer) who has experience suing the government.
I should add that if there was probable cause, but the probable cause turned out to be based on false or incorrect evidence, then the state should have set your son free as soon as it realized that. If they didn't, that's a wrongful detention.