The Denver man who fatally shot a woman and wounded a man near Coors Field because he was angry about how they were speaking to their dog has a history of untreated mental illness and childhood abuse, his attorneys said Monday at the start of his jury trial.

Michael Close, 38, suffered a mental break and “did not know what he was doing” when he opened fire with an AK-47 rifle on June 10, 2020, killing 21-year-old Isabella Thallas and wounding her boyfriend Darian Simon outside Close’s Ballpark apartment on North Fox Street while the couple encouraged their dog to defecate, his attorneys said.

Close has pleaded not guilty by reason of insanity in Denver District Court to charges of first-degree murder and attempted first-degree murder.

His public defenders told jurors he committed the shooting, but argued during opening statements that Close should nevertheless be found not guilty because he was legally insane at the time of the attack.

“Mike … had a mental break,” Deputy Public Defender Sonja Prins said. “He disassociated. He was outside of his head. He did not consider anything. He had a mental break and he did not know what he was doing when he shot Isabella Thallas and Darian Simon.”

Prosecutors with the Denver District Attorney’s Office dismissed that argument and told jurors that Close was sane during the shooting and acted on long-boiling rage because he felt disrespected in other areas of his life.

“He was stewing and he was welling with anger inside of him,” Deputy District Attorney McKenna Burke told the jury.

Close had broken up with his girlfriend of nearly five years in January 2020, then lost a series of jobs working at bars and a marijuana dispensary because of the COVID-19 pandemic, Prins said. He’d visited with his ex-girlfriend on June 9, 2020, where he drank alcohol and argued with her for much of the night. On the morning of June 10, 2020, he texted his ex-girlfriend that one of his dogs was attacked by other dogs at a dog park. He said he planned to “execute” the owners of those dogs with a knife or a gun.

Simon and Thallas had nothing to do with the alleged incident at the dog park. They just happened to walk their dog outside of Close’s ground-floor apartment that day and paused to encourage their dog to defecate, Burke said.

Close became enraged by the way Simon spoke to the dog. He yelled out the window at the couple, then retrieved the AK-47 from another room, returned to the window and fired the gun 24 times, Burke said. Thallas was shot in the back and killed instantly, she said.

“She never saw it coming,” Burke told jurors.

The shooting was recorded by a building surveillance camera. Close used then-Denver police Sgt. Dan Politica’s personal AK-47 in the attack.

Politica was Close’s longtime friend; police said Close took the gun without the sergeant’s permission. Close also texted Politica immediately before the attack, saying that he was going to murder someone, and then after, saying he had “done something really bad.”

Politica later resigned from the police department.

After the shooting, Close called his ex-girlfriend and confessed. He was crying and upset, she testified Monday. He told her he was going into the mountains and asked her to take care of his dogs. He then got in his SUV and drove west. He was pulled over that evening on Highway 285 by deputies with the Jefferson County Sheriff’s Office and arrested.

Prins said Close had planned to die by suicide. He was pulled over with both the AK-47 rifle and a pistol in the car. She noted Close had previously attempted suicide as a teenager, was diagnosed with a personality disorder for which he did not receive treatment, and sometimes hallucinated a shadowy figure. After an abusive childhood, he was taken in by a couple at age 17 after his biological father gave up custody, she said.

Prins added that Close’s friends had been increasingly worried about his mental health before the shooting, and had taken steps to encourage him to attend therapy.

The jury trial is expected to last through Friday.

Correction 12:30 p.m. Sept. 22, 2022 This story was corrected to reflect that Dan Politica does not work for Colorado Springs police. A department spokesperson says Politica has never worked for the agency.