The mistress of Patrick Frazee — the Colorado man accused of murdering his fiancée, Kelsey Berreth, with a baseball bat and burning her body last year — testified Wednesday that the woman's last words before she was bludgeoned to death were "please stop."

Krystal Kenney, a nurse from Idaho who is the key witness in Frazee's murder trial, said at the courthouse in Teller County that the 33-year-old man, of Florissant, manipulated her, and explained how she ultimately helped clean up the mess made after Berreth died last Thanksgiving.

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Berreth, 29, was last seen nearly a year ago near her home, around two hours south of Denver, with the daughter she shares with Frazee. Her body has never been found, despite several searches, and Frazee has pleaded not guilty to first-degree murder in her death.

Under a plea agreement, Kenney has pleaded guilty to evidence tampering for moving Berreth's cell phone. She agreed to testify against Frazee under a plea agreement, and on Wednesday spent six hours describing their 13-year relationship — which included a pregnancy that Kenney says she was forced to abort.

“He went from being someone who I loved and cared for and is one of my best friends,” she said in court, according to The Denver Post. “He said his little girl was being abused. I know it was wrong, but I didn’t know what to do and I didn’t make the right decisions.”

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Kenney met Frazee in 2006. The two dated on-and-off, and kept in touch. Kenney claims Frazee pulled her away from a family of her own, and in 2016, she became pregnant with his child. She aborted the baby — she claims Frazee told her "I guess you’re a baby killer or you’re not" — and later learned about Berreth and the daughter she had with Frazee.

“My jaw just about hit the floor,” Kenney said, claiming that when she confronted Frazee, he said Berreth was an unstable alcoholic who abused their daughter. One day in October 2018, when Kenney watched the girl, she said Frazee scolded her for every little thing.

“That’s when I had the thought that Kelsey probably wasn’t doing anything wrong,” Kenney said. “She just couldn’t do anything right.”

Frazee kept telling Kenney she needed to help him “take care of the problem,” Kenney testified. She said she knew this meant killing Berreth. He allegedly plotted several ideas of how Kenney could kill Berreth, one of them being with a poisoned caramel macchiato. Kenney said she would take a weapon to wherever Berreth was but never followed through.

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On Thanksgiving 2018, Kenney said she received a call from Frazee telling her she "had a mess to clean up" in Colorado. She drove 12 hours with cleaning supplies in her car, and said she didn't think much else. When she got to Berreth's condo, she said there was dried blood covering the walls, and the home was covered in bloody footprints.

“I didn’t know that he was capable of that,” Kenney told the court. “I didn’t know that he was capable of what happened, and I didn’t do anything to stop it.”

Kenney and Frazee spent 12 hours cleaning the condo and destroying evidence, she said. Kenney claimed they took a container that had Berreth's body inside and burned it.

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Frazee's mistress took Berreth's phone from the condo and drove it to Idaho, where it pinged a cell phone tower. She was found by law enforcement, and initially lied to the FBI, but eventually agreed to cooperate.

On the witness stand, she said Frazee told her Berreth's last words were "please stop."

The Associated Press contributed to this report.