Her body has not been found. Police believe she was killed at her home in the small mountain city of Woodland Park on or around Thanksgiving. Prosecutors have filed additional charges against Frazee, including tampering with a deceased body and two charges of committing a crime of violence.
Teller County District Judge Scott Sells hearing the case ruled there was sufficient evidence to bind Frazee over for trial, and had set an April 8 arraignment date for him to enter a plea.
FOX31 will have a crew inside the courtroom Tuesday for the preliminary hearing.
In testimony Tuesday from Frazee's preliminary hearing, CBI Agent Greg Slater testified that Krystal Lee Kenney once brought Berreth a Starbucks drink claiming to be a neighbor after Frazee had suggested she drug the drink, according to KUSA.
Investigators testified that Frazee began planning Berreth's death in September and enlisted an Idaho woman who told authorities they had been having a romantic relationship for several months before that.
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.
Another witness, Patrol Commander Chris Adams of the Woodland Park Police Department, played a recording of a November phone call with police in which Frazee said that Berreth had called him to end their relationship.
The couple has a 1-year-old daughter, Kaylee, who is now in the custody of Berreth's parents. Berreth told Slater that her daughter said she had seen Frazee the night before and had gotten medicine for his stomach ailment before returning to her home.
Berreth, a 29-year-old flight instructor, was last seen on November 22 near her home in a mountain town near Colorado Springs, south of Denver.
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Kenney told police she wanted to please Frazee and feared that he would harm her or her family if she did not cooperate. Police said there is no evidence that the girl was abused by her mother or anyone else.
Kenney told police that Frazee had wrapped a sweater around Berreth's head before beating her to death with a baseball bat and stashed her body on a ranch.
"You got a mess to clean up", Frazee said according to Kenney's account.
The filings also state that "Frazee had the motive to kill Kelsey in that he wanted full custody of KB or Kelsey to leave KB with him and Kelsey would not agree".
Prosecutors' evidence also includes cellphone tower data, suggesting Berreth's phone was in the possession of either Frazee or Kenney after November 22, the date Frazee told police he last saw Berreth.
Police searched Berreth's Woodland Park home after she was reported missing December 2 and found no evidence inside the home.
In early December, investigators examining Berreth's bathroom found blood in the toilet, the bathtub exterior, the bottom of a trash can, the walls, floor, a towel rack, the vanity and an electrical outlet, according to Slater. The child has remained with them while the criminal case against Frazee proceeds.
She said Frazee later told her he planned to throw the remains in a dump or river.
Prosecutors filed two murder charges because they have different theories.
Frazee, 32, has not entered a plea and has been jailed since his arrest.