The petitioners were convicted for alleged conspiracy to violate the National Prohibition Act by unlawfully possessing, transporting, and selling alcohol.
Three of those men were arrested and charged with unlawfully possessing and selling a firearm; the fourth man was at large, the police said.
During the day, a state-appointed disciplinary panel ruled that he should be dismissed, saying he "knowingly and unlawfully possessed a controlled substance."
He was also charged with unlawfully possessing a loaded 9-millimeter handgun.
He had denied the charge, but admitted another of unlawfully possessing a firearm.
Gray previously served time in New Jersey state prison from 1996 to 2000 for theft, burglary, aggravated assault and unlawfully possessing a weapon.
In September 1993, he was convicted of unlawfully possessing a firearm and trespassing and sentenced to 30 days in the county jail and one year's probation.
He was found with an open container, unlawfully possessed alcohol, and various drug paraphernalia.
The Bureau is also involved in programs aimed at reducing gun violence in the United States, by targeting and arresting violent offenders who unlawfully possess firearms.
On 4 April 2007, the Court of Appeal of New Zealand overturned his convictions for unlawfully possessing a firearm.