Transcript for Prosecutors reveal chilling details of fiance's alleged murder
Those chilling details about the Colorado mother who vanished on Thanksgiving. Prosecutors reveal how her fiance murdered her and used a nurse's help to help cover it up. Kayna Whitworth is covering the case from Denver. Good morning, kayna. Reporter: George, good morning. So, accused murderer Patrick Frazee really showed no emotion during the eight hours of testimony yesterday but at times he sort of dropped his head when investigators described in horrifying detail how they believe he killed Kelsey Berreth. Accused murderer Patrick Frazee led into a packed courthouse wearing a ballistic vest and handcuffs as gruesome new testimony comes to light about the role that the Idaho nurse Krystal Lee Kenney played in the murder of Kelsey Berreth allegedly last seen on November 22nd with her 1-year-old daughter Kaylee on the surveillance video at safeway. According to an agent for the Colorado bureau of investigation, Kenney told investigators Frazee called her on November 22nd to say she had hi mess to clean up and that Kenney said she knew Frazee had killed Berreth. Patrick kills Kelsey in a horrific manner. With a bat in the back of the head as Kelsey is sniffing candles with a blindfold over her eyes. Kaylee was in the back room of Kelsey's condo when Kelsey was murdered. Reporter: The agent testified that Kenney said Frazee then went to Thanksgiving dinner with his family and then Kenney claims she cleaned up the crime scene two days later then watched Frazee burn a black tote bag she believed contained Kelsey's body. Kenney, Frazee's mistress allegedly told investigators she feared for her children's safety after veiled threats from Frazee. So she said she complied but claimed she intentionally left behind evidence of the murder for investigators to find. We wouldn't even know where the murder happened in the apartment even which room or where it happened at all without her testimony. Reporter: But it was Berreth's parents who investigators say first notified them of blood splatter in their daughter's bathroom. Nearly two weeks after she disappeared. The agent testified Frazee said Berreth was an abusive mother despite police saying they have no evidence of that and that Frazee asked her to kill Kelsey. Once even suggesting that she poison Kelsey's favorite Starbucks coffee, a caramel cchiato. Patrick Frazee contacted Krystal Lee in Idaho on three separate occasions, had her come to Colorado to murder Kelsey. Reporter: Kenney allegedly admitting she did end up bringing the coffee to Kelsey posing as a new neighbor but said she didn't poison it. Now, Krystal has also pleaded guilty to Kelsey's cell phone and you have to remember that Patrick told investigators the last time he saw Kelsey Berreth was on Thanksgiving. But prosecutors are using cell phone location data to prove Patrick and Kelsey's phones were in the same location days after that. Now, guys, Patrick has not entered a plea but he will be arraigned in April. So chilling. It sure is. Thank you.
This transcript has been automatically generated and may not be 100% accurate.