Colorado police plan to search a landfill for the remains of a woman whose fiance is charged with murdering the mother of his 1-year-old child.

The search of the landfill in Fountain is scheduled to begin Tuesday. The Woodland Park Police cautioned in a written statement that it could take weeks or even months to complete their search for Kelsey Berreth's remains and other evidence.

It was not clear on Friday what led police to search the site, which is about 40 miles from Berreth's home.

The 29-year-old flight instructor was last seen on Nov. 22 near her home in a mountain town near Colorado Springs, south of Denver. The search for Berreth did not begin until Dec. 2, when her mother reported her missing.

Berreth's fiance, Patrick Frazee, was charged with murder and solicitation to commit murder more than a month later. Frazee, 32, has not entered a plea.

Dramatic court testimony during a Tuesday hearing revealed that Frazee's girlfriend told police he repeatedly asked her to kill Berreth. Investigators told a judge that Kenney told police Frazee admitted beating Berreth to death with a baseball bat.

The woman, Krystal Lee Kenney, is cooperating with prosecutors as part of a plea agreement. She is also required to testify against Frazee.

The 32-year-old former nurse from Idaho has pleaded guilty to evidence tampering, admitting she moved Berreth's cellphone.

Kenney told police that Frazee demanded she come to Colorado and clean up blood spattered on the floor, walls and furniture of Berreth's home.

Kenney said she then watched as Frazee burned Berreth's body on his property, according to testimony. She told police that Frazee planned to throw the remains in a dump or a river.

Prosecutors' evidence also includes cellphone tower data, suggesting Berreth's phone was always in the possession of either Frazee or Kenney after Nov. 22, the date Frazee told police he last saw her.

Prosecutors have not discussed any theories on why Frazee would kill Berreth. Her parents argue in a wrongful death lawsuit that they believe Frazee wanted full custody of the couple's 1-year-old daughter. The child has remained with them temporarily while the criminal case proceeds.