[Head-Space]

The fellow is a convicted felon, released "on supervision". He can't legally possess a gun. Therefore, registering it would be a violation of his 5th Amendment right against self incrimination. SO, while he may be charged, he cannot be convicted, legally. The charge is a bargaining chip, The DA knows he can't make it stick, but hopes the guy's lawyer (public defender?) will not realize it, and they can "bargain" away the charge for some concession from the accused, without losing anything real.

This assumes, the accused is legally prohibited from owning a gun.

"If it weren't for lawyers, we wouldn't need attorneys."