Thanks for posting. Interesting case. That being said, Federal Charges could be brought. I'm surprised they weren't.
Anyone who has been convicted of a felony is banned by federal law from ever possessing "any firearm or ammunition." Specifically a person "convicted in any court of a crime punishable by imprisonment for a term exceeding one year" cannot possess any firearm in any location. 18 U.S.C. 922(g) is the federal law that prohibits anyone ever convicted of any felony to ever possess any firearm either inside or outside of his home. The federal punishment for felon gun possession is up to 10 years in prison.