What are the US laws regarding undercover work? For example, let's say a reporter joins a criminal organization but is undercover, and is caught at a crime scene with the gang but didn't actually do anything illegal? Would they still be considered guilty by association, even if they could prove they didn't do anything?

I believe there's a hero in all of us that keeps us honest, gives us strength, makes us noble, and finally allows us to die with pride, even though sometimes we have to be steady and give up the thing we want the most. Even our dreams. -- Aunt May, Spider-Man 2