Setting USA (technically somewhere in the Deep South but it's a Federal case so I don't think that matters), some time at the height of the Civil Rights movement.
I have a (white) man who witnessed (and tried to stop) the lynching of two young black men who had been registering black people to vote and generally pissing off people all over the place. He was severely assaulted but not killed in the process. The local police were at the very least turning a blind eye if not openly collaborating with the mob in the lynching and have told him in no uncertain terms that he didn't see who attacked him or who lynched the boys. However he's stubborn enough to keep making a fuss and a federal case about the breaching of his civil rights is brought. Consequently the FBI have decided they better do something or he might not still be alive when the trial happens and that would be bad. The exact details of when and where are as yet to be decided, but I think that's the relevent stuff.
I need to know who would be protecting him. I think it would be the US Marshals but I'm not sure since all the stuff I can find refers to the 1970 Witness Protection Act or the 2007 proposed amendment (but I think that only applies to State and local witnesses anyway). Both of which are too late for my story, however I do know that when Robert Kennedy sent people to protect James Meredith who was registering at the university of Mississippi he didn't want the locals to do it so he sent in the Marshals. Plus of course they refer only to witnesses and my guy is both a witness (in the case about the civil rights of the black kids) and a victim.
I've searched using terms such as 'federal case' 'protection of witnesses' 'protection of victims' etc in various combinations but mostly I get the witness protection act. I tried putting in some date terms but then I either got nothing relevent at all or more about Meredith.