Denver -- After urging a woman he was having an affair with for months to kill his fiancee, investigators say a Colorado man did it himself on Thanksgiving Day -- bludgeoning his fiancee to death with a baseball bat and then calling the woman to help clean up blood. The grim details revealed in a Colorado courtroom Tuesday provided the first public account of what led prosecutors to charge Patrick Frazee with murder and other charges in the death of Kelsey Berreth, the mother of his 1-year-old daughter.

Colorado Bureau of Investigation Agent Gregg Slater testified Tuesday that Krystal Jean Lee Kenney described the scene inside Kelsey's Berreth's home as "horrific." Kenney told police she brought gloves, a protective body suit and trash bags from her home in Idaho at Frazee's request.

Frazee is charged with murder and solicitation to commit murder. Berreth's body has not been found since she disappeared on Thanksgiving Day, Nov. 22.

Authorities had released little information about their case against Frazee until Tuesday's hearing, which requires prosecutors to convince a judge that their evidence merits a criminal trial. After the hearing that spanned hours, a judge ruled that the case could proceed, reported CBS News' Jamie Yuccas.

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Testimony revealed that police initially found no evidence of foul play inside Berreth's home but later discovered traces of blood belonging to the 29-year-old flight instructor in several places in her bathroom.

The case relies heavily on the cooperation of Kenney, a 32-year-old nurse from Idaho, who has pleaded guilty to helping thwart the investigation by tampering with evidence in the case. She has agreed to testify against Frazee.

Dramatic testimony on Tuesday revealed that Kenney admitted beginning a romantic relationship with Frazee in March 2018 and that Frazee tried to convince Kenney to kill Berreth three times, Slater said. Slater testified that Kenney told police Frazee claimed that Berreth was abusing the couple's daughter, although Slater said there was no evidence that was true.

Kenney said Frazee suggested multiple ways that she could kill Berreth, including poisoning her coffee or striking her in the head with a metal rod and a baseball bat, Slater said.

Kenney told police she wanted to please Frazee and feared that he would harm her or her family if she did not cooperate. Kenney told police she did not follow through on any of Frazee's plans, Slater said.

"Krystal tells investigators that she didn't comply with any of those, and that the last time she was here on October 21 she sat and said 'I can't do this…' and tells Patrick 'I can't do this,'" prosecutor Jennifer Viehman told reporters after the hearing.

Court Update: Patrick Frazee’s Lover Was Told To Drug Kelsey Berreth’s Coffee https://t.co/SBvrvWc4kZ pic.twitter.com/s6Ssu85VLt — CBSDenver (@CBSDenver) February 19, 2019

Kenney said Frazee suggested that she drug Berreth's favorite coffee drink, a caramel macchiato, and give it to Berreth, reports CBS Denver. She also told police that as a nurse she carried the drugs that she could use to poison the coffee. Police said Kenney admitted to buying the drink to give to Berreth but that she didn't put any drugs in that drink.

Kenney's friend Michelle Stein told CBS News this month Kenney confided in her and said Kenney feared for her life.

"I will just tell you Krystal was very, very scared," said Michelle Stein. "Krystal's a very level-headed, kind, fun-loving, happy-go-lucky person. She's a tough cowgirl. But she was absolutely scared and extremely upset."

Kenney said he was angry each time she failed to act. She loved Frazee and wanted to make him happy but could not hurt Berreth, Slater said.

Kenney received a call from Frazee on Nov. 22 demanding that she drive to Colorado, Slater said.

"You got a mess to clean up," Frazee said according to Kenney's account to police.

She said she arrived two days later and found a "horrific" scene with blood spattered on the walls and floors of Berreth's townhome, Slater said.

Kenney told police that Frazee had wrapped a sweater around Berreth's head, telling her he wanted her to guess the scent of candles as a ruse, before beating her to death with a baseball bat and stashing her body on a ranch. After she cleaned the house, Kenney said she went with Frazee to retrieve Berreth's body and watched as Frazee burned it on his property along with the wooden bat, Slater said.

She said Frazee later told her he planned to throw the remains in a dump or river.

Prosecutors have not revealed a motive, but Berreth's parents argue in a wrongful death lawsuit filed last week that they believe Frazee wanted full custody of the couple's 1-year-old daughter. The child has remained with them while the criminal case against Frazee proceeds.

Berreth's mother, Cheryl, said Frazee lied during a Dec. 2 phone conversation when he said he and Berreth "broke up on/or about Thanksgiving Day" and agreed at a Cracker Barrel restaurant in Colorado Springs to split custody of their daughter.

When Cheryl pressed Frazee for details about her daughter's whereabouts, he suggested that "Kelsey may have flown somewhere with a friend or co-worker."

"Typically, if Kelsey was going to travel, we knew ahead of time," Cheryl told CBS News in December.

Berreth's body has not been found. Investigators initially said she was last seen on surveillance video with the couple's daughter at a grocery store near her home in Woodland Park, a mountain town near Colorado Springs, south of Denver.

Police later found footage on a neighbor's surveillance camera showing Berreth, Frazee and their daughter at the entrance of Berreth's townhome later that afternoon.

Much of prosecutors' evidence hinges on cellphone tower data, suggesting Berreth's phone was in the possession of either Frazee or Kenney after Nov. 22, the date Frazee told police he last saw Berreth.

Frazee, 32, has not entered a plea and has been jailed since his arrest. Prosecutors this week added a charge accusing Frazee of tampering with a deceased body and two charges of committing a crime of violence, which would let the state request a harsher penalty on conviction.