Witnesses: Man accused of killing wife believed she strayed

Friends of a man accused of killing his wife told a jury Wednesday they engaged in a consensual sexual relationship with the couple.

Courtney Rush and Randall Cannon said Humberto Diaz accused Rebecca Diaz of sleeping with Cannon, which violated an agreement among the four.

Rush and Cannon, her common-law husband, met Diaz and his wife in early 2015 after responding to an ad for open couples on Craigslist, s he testified.

Rush said the sexual relationship tapered off over the summer when the defendant started acting "weird."

"He'd text me and talk to me sexually and I didn't like that because it was one of those things," she said. "I don't want to talk without my husband there."

Humberto Diaz, 33, is charged with first-degree murder in the Nov. 8, 2015, death of Rebecca Diaz, 26, who was shot once in the side of the head and once in the face.

Police said Diaz pulled a gun on his wife after an argument where they ended up fighting on the roof of the two-story home they shared in a semi-rural part of southeast Oklahoma City.

In a 911 call played for jurors, the defendant tells a dispatcher he shot his wife because she was trying to cover up a crime. He also told the dispatcher his wife was going for a gun when he shot her.

"She had been trying to cover up a crime that she did with a drug dealer and my daughter," he said. "I have evidence. She tried to get me arrested for it."

Defense attorneys contend Diaz is not guilty on grounds he was insane at the time and did not know right from wrong. Such a defense is exceptionally rare at a jury trial.

Diaz was discharged from the Air Force after testing positive for drugs in August 2015, according to records from his divorce. He also attended a weeklong, inpatient drug treatment program at Integris Baptist Medical Center.

The victim's relationship with Diaz was tumultuous, exacerbated by substance abuse, according to friends, as well as police and court records. His verbal and physical abuse grew worse as his drug problem progressed.

Cannon testified about how Humberto Diaz grew paranoid and accused his wife of cheating on him and of trying to poison him.

The witness described a conversation he had with Humberto Diaz two nights before the shooting.

"He said he needed to get away or he was going to kill her," Cannon testified.

On the evening of her death, Cannon told the jury Rebecca Diaz called his wife screaming. "He was hurting her," he said. The couple rushed to the Diaz home, where the defendant was pacing back and forth on the roof. He warned them not to go inside, Cannon said.

The trial continues Thursday in the Oklahoma County courtroom of District Judge Ray C. Elliott.