CRIPPLE CREEK, Colo. — The key witness against a rancher convicted of killing his fiancee will be sentenced Tuesday for tampering with evidence in the case.

Krystal Lee Kenney, the former Idaho nurse, reached a plea deal with prosecutors requiring her to testify against Patrick Frazee in Kelsey Berreth’s death.

She faces up to three years in prison for taking Berreth’s cellphone back to Idaho to try to make it look like Berreth had left Colorado.

Berreth’s body has never been found. Kenney, who had an intimate relationship with Frazee, testified that Frazee told her that he beat her to death with a baseball bat and that she cleaned up the crime scene.

She also said Frazee tried to get her to kill Berreth herself three times.

Frazee was found guilty of two counts of first-degree murder, one count of tampering with a body and three counts of solicitation to commit murder.

He was sentenced to life in prison without the possibility of parole, plus 156 years.