Police believe she was killed at her home in Woodland Park.
The preliminary hearing for Patrick Frazee, who is accused of killing his fiancée Kelsey Berreth, is set to begin Tuesday morning in a Teller County courtroom, where prosecutors will try to show the court they have enough probable cause to continue with the felony charges against him.
Frazee has yet to enter a plea and has been in jail since his arrest took place in December.
He later burned her body in a water trough, according to testimony at a preliminary hearing in Cripple Creek, west of Colorado Springs.
Gregg Slater, an agent with the Colorado Bureau of Investigation, testified that Frazee blindfolded Berreth and beat her to death by hitting her on the head with a baseball bat, Jon Sarche, a public information officer with the Colorado Judicial Branch, confirmed to Reuters.
A woman who has pleaded guilty to helping thwart the investigation into a Colorado woman's disappearance told police that she was in a romantic relationship with the man now charged in his fiancee's death.
Slater testified that Kenney would later tell investigators that Frazee had "wanted Krystal to get rid of Kelsey" and even offered a possible avenue to target the flight instructor: a poisoned caramel macchiato. She waited for Berreth, but still couldn't do it, Slater said. It was there that prosecutors presented evidence against Frazee and issued additional charges of tampering with a deceased body as well as two charges of committing a crime of violence.
Kenney took Berreth's phone to Idaho, where she sent text messages to Frazee and Berreth's employer posing as the dead woman then burned the phone, the investigator said.
Berreth, who had a 1-year-old daughter with Frazee, was last seen alive on Thanksgiving Day, and her body has not yet been found.More news: Asda and Sainsbury's merger could SELL OFF 'significant' number of stores
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Cell phone records produced at the hearing showed calls between Frazee and Berreth around the time of her disappearance.
Berreth, 29, vanished last Thanksgiving near Woodland Park, a city between Denver and Colorado Springs. Kenney told police she did not follow through on any of Frazee's plans, Slater said. Police said Kenney admitted going to Berreth's home to give her a coffee in September.
"I learned Patrick Frazee had committed a homicide on approximately November 22, 2018, in Teller County", Kenney said in a statement read in court.
"You don't know how hard it is to have Thanksgiving dinner after killing her", she recalled Frazee telling her, according to Slater.
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".
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.
She said Frazee later told her he planned to throw the remains in a dump or river. Berreth went missing Thanksgiving Day.
Frazee faces two counts of first-degree murder and three counts of solicitation to commit murder in the first degree in addition to the charges added on Tuesday. They are in a custody battle over the young girl with Frazee and his mother.
Defense attorneys also highlighted a lack of blood or other physical evidence detected in Frazee's truck and questioned the Berreth family's access to Kelsey's townhome following initial police searches.