Yes, but the guy made something and was convicted, so he has the potential to commit a crime again, and possibly he want the ballistic vest for the "job".
Makes sense for me, but i am not an American Judge to judge if it right or wrong.
But if he was convicted for a serious offense, then i believe he must not even be allowed to posses a big kitchen knife.
For a Law abiding Citizen, i can't see why he may not be allowed to own one in US.
Here we can have them.