PITTSBURGH (KDKA) — The man shot and killed by Pittsburgh Police Sunday at his home in Larimer never should have had a gun in his hands.

Online criminal court records in Allegheny County show Christopher Thompkins went to prison for shooting and killing someone in 1994. That conviction means he should not have been in possession of a firearm on Sunday when investigators believe he was firing the gun to scare off an intruder.

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In November of 1994, police were called to an apartment building on West North Avenue for a report of a domestic disturbance. When they arrived, they found Ronald Cunningham shot twice in the chest. He died at Allegheny General.

Cunningham was a happily married father of four boys. He just happened to be at the apartment working as a handyman and intervened when Thompkins pulled a gun on his ex-wife, Brenda Richmond.

She gave an interview to KDKA’s Ralph Iannotti after the 1994 incident.

Richmond said, “Ronald Cunningham tried to block him from shooting me. He was like blocking him so he couldn’t shoot me and he shot him. Shot him twice. Not once, twice. Shot him dead in the chest.”

Richmond went on to say, “I want to let the world know that Ronald Cunningham is a hero. He saved my life. And, believe me, domestic violence does not get any better if you are in a situation like that. The best thing to do is get out.”

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In March of 1997, Thompkins was convicted of criminal homicide and sentenced to seven to 15 years in prison. That conviction made it illegal for him to ever possess a firearm.

Fast forward to Sunday at 4 a.m. Pittsburgh police were called to Thompkins’ home on Finley Street for a report of a home invasion. Richmond was there.

According to the criminal complaint, she told police Juan Brian Jeter-Clark broke in and was standing over their bed. She reported that Thompkins said to give him her gun. Investigators say they believe Thompkins was firing the gun to scare Jeter-Clark.

When police arrived, they saw a man coming down the stairs firing shots in their direction. Police returned fire, killing Thompkins.

In 1997, on the same date of Thompkins’ homicide conviction, he pleaded nolo contendere in another case for possessing a firearm when he was prohibited under the law.

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Sunday’s case is still under investigation. The two officers involved are on administrative leave, which is standard protocol. Jeter-Clark is charged with criminal trespass.