An Army veteran who has repeatedly been hospitalized for treatment of a mental illness and has threatened to harm police and others at the Veterans Affairs Medical Center in Buffalo has been arrested by federal agents for unlawfully keeping a shotgun at his home.

The 36-year-old City of Tonawanda man also rented an assault-style rifle at a North Tonawanda gun range and admitted to a doctor that he had thought about hurting people at the Erie County Fair and Canal Fest, events that attract tens of thousands of people, according to documents filed in U.S. District Court.

Christopher M. Simmance this week was charged with felony criminal possession of a weapon because it is illegal under federal law for someone who has been committed to a mental health institution to possess a weapon.

His case highlights a key piece of the debate taking place in New York and across the nation over gun laws, with advocates on both sides of the gun-control argument seeking better enforcement of laws meant to keep weapons out of the hands of emotionally disturbed persons.

Once someone has been committed to a hospital for treatment of a mental illness, the person is prohibited by federal law from having any kind of firearm. The U.S. Attorney’s Office in Buffalo wasn’t able to provide data on the number of arrests made under this charge in the area.

In Simmance’s case, his concerned father contacted City of Tonawanda police in November 2011 and asked officers to remove the 12-gauge, pump-action Remington shotgun that Simmance had at his apartment.

City of Tonawanda police have arrested Simmance three times – for disorderly conduct and petit larceny in 1994, and disorderly conduct in 2010 – and have checked on his welfare on other occasions, police officials previously told The Buffalo News.

Mark A. Simmance asked officers to take his son’s shotgun because he believes Simmance suffers from post-traumatic stress disorder, or PTSD, and he shouldn’t have a weapon, according to an affidavit filed in federal district court by Special Agent Thomas Rodriguez of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

Christopher Simmance served in the Army from January 1998 to January 2001, leaving active duty with the rank of specialist, according to Army records obtained by The News.

Simmance, a member of the Occupy Buffalo movement in 2011, has told reporters from The News and other media outlets that he served in Iraq and Afghanistan and he was wounded in combat.

The News reported in late 2011 that Army records do not support Simmance’s claims of seeing action in a war zone, and Simmance’s mother told the newspaper she believed her son’s mental illness led him to exaggerate his service record.

Simmance was involuntarily committed to the VA hospital twice in May 2009 and once in April 2010, Rodriguez wrote in his affidavit.

Last July, when VA police were called to the emergency room to escort Simmance to another part of the hospital, Simmance became upset and threatened to shoot the officers with ammunition that would pierce their bulletproof vests.

The next day, Simmance’s mother, Denise, contacted City of Tonawanda police because she was alarmed about several items she found in her son’s apartment while he was undergoing a psychiatric evaluation at the VA hospital.

Denise Simmance turned over to police a machete, an “Army Ranger” knife, a law-enforcement-style baton and 21-round, .223-caliber ammunition magazines.

Simmance’s mother also gave police a journal that contained written threats against a janitor and another person at the VA hospital. Simmance described wanting to shoot the janitor in the head.

When VA police questioned Simmance, he said he was asked by a therapist to write down his thoughts but he didn’t recall writing those threats.

He said he did own a shotgun, which he said he used to hunt on a property in Warsaw, but his father had taken the weapon from him.

Earlier on the same day he was interviewed by the agents, Simmance told a doctor he thought about hurting people at the Erie County Fair and Canal Fest, but he later told the agents he wouldn’t harm anyone.

Last August, ATF agents talked to an employee of the Niagara Gun Range in North Tonawanda, which allows patrons to rent and shoot a variety of weapons. The employee told the agents range records show Simmance rented an assault-style rifle there in March 2011.

Simmance is not charged with renting this rifle, nor with having the ammunition clips at his apartment.

The charge covers the shotgun, and in order to bring the illegal-possession charge, federal agents and prosecutors had to show the weapon crossed state lines at some point in its history.

Simmance’s shotgun was manufactured in New York but was shipped to a Kmart distribution center in Warren, Ohio, before it was returned to New York and sold at a Kmart store in Batavia.

It’s not clear from the criminal complaint why, if police learned in November 2011 that Simmance had the shotgun, charges weren’t brought until this month. Barbara Burns, a spokeswoman for the U.S. Attorney’s Office in Buffalo, said she couldn’t answer that question because it is part of an ongoing investigation.

Frank J. Christiano, resident agent in charge of the ATF, said Simmance’s arrest was the culmination of a lengthy investigation by the ATF, City of Tonawanda police, VA police and the VA’s Office of Inspector General, but he declined further comment.

Simmance was taken into custody on Sunday. A detention hearing held Thursday before U.S. Magistrate Judge Jeremiah J. McCarthy was adjourned until April 4.

Assistant U.S. Attorney John M. Alsup is prosecuting the case.

Simmance faces a maximum sentence of 10 years in prison if convicted of the felony weapons charge. He remains in the temporary custody of the U.S. Marshals Service.