This is probably the wrong forum. This seems like a General Gun Discussion thing.
If there actually are never charges filed, and the government does not meet their burden at trial if those charges are
filed, then it is an unconstitutional abuse of power and he will almost certainly be able to get recourse of some sort in court.
However, if he actually has been into some bad stuff, police are, as far as I know, allowed to confiscate weapons immediately prior to charges or while the charges are being crafted. According to the news article:
Neighbors said Adams was a gun collector, and some heard he was a licensed gun seller, too.
Federal investigators confirm that. However, they're also investigating him for possible gun smuggling, tax evasion and violating importation laws.
Since we don't have access to the case the Feds have against him, we really aren't in a position to have an opinion on it. He is innocent until proven guilty, and if the government cannot overcome that presumption, I will join the outcry and even donate to any legal fund for him. However, I will not prematurely cry oppression when I don't know all the facts. I don't want to be in the position of having defended a gun smuggling tax evader if he turns out to be guilty.