PITTSBURGH (AP) — Police officers responding to a burglar alarm fatally shot a homeowner, who had grabbed a gun when he spotted an intruder, after shots were fired in their direction as they arrived at his house.

Until ballistic and other evidence can be reviewed, police said they couldn't say who fired the shots while officers were on Christopher Thompkins' front porch. But police Acting Chief Scott Schubert called what happened "a horrible chain of events."

Thompkins, 57, died in the gunfire before dawn Sunday. Police did not report finding a gun on the intruder, identified as Juan Brian Jeter-Clark, 23. Jeter-Clark was charged with criminal trespass but could face additional counts.

Thompkins' ex-wife, Brenda Richmond Thompkins, said she was in bed with him when they spotted an intruder standing nearby. She said he grabbed her gun, not realizing police had already been summoned by their burglar alarm company, and then chased after the intruder down some steps to the home's front door because he was worried about his blind mother, who uses a wheelchair and lives downstairs.

"Christopher was saying, 'My mom, my mom, my mom, my mom,'" said Richmond Thompkins, who was divorced from Thompkins years ago and had reconciled with him.

She said she fled out the second-floor bedroom window while calling 911.

"I don't know how they started firing because I wasn't there," she said. "I was going, I was running for my own life."

Once out the window she yelled at police, "Please don't shoot me. I'm a victim. The guy's still in here."

Thompkins was sentenced to seven to 15 years in prison for murder for shooting a handyman who tried to break up an argument between the couple in 1994. Thompkins had said the gun fired accidentally.

Court records show the sentence was vacated by an appellate court, though Richmond Thompkins said Thompkins still wound up serving 10 years in prison. After getting out of prison, Thompkins worked for a cleaning company and later as a dialysis technician.

Richmond Thompkins said she doesn't believe Thompkins purposely fired at police and believes he would have dropped the gun had officers yelled out to identify themselves.

"They shot the wrong guy. He didn't want to hurt no cops," she said in a telephone interview. "He was trying to save his mother."

The acting police chief said it was difficult to find the words "to describe the amount of empathy that I have for both the family of Christopher Thompkins and the two officers (who) were involved in the shooting."

Court records didn't list an attorney for Jeter-Clark, who remained in the county jail on Monday and couldn't be reached for comment.

The Allegheny County district attorney is reviewing the shooting.

The 911 call and video from the scene have been reviewed, police said, and interviews have been scheduled with the officers. The officers are on leave pending the outcome of the investigation, which is standard practice. They haven't been publicly identified.

Richmond Thompkins said three men were seen lurking on their block in recent days and one of them looked like Jeter-Clark. She said it's possible the intruder entered the home because Thompkins recently bought a new car.

The intruder called Thompkins "old head," a slang term for an older person, she said.

"You know how these kids are," she said. "When they think you got something (valuable), you know how they are."