Following Kelsey Berreth's disappearance on Thanksgiving Day 2018, her ex-fiancé Patrick Frazee was officially charged with her murder. He is currently being held in a Colorado prison as he awaits the beginning of his trial later this month, but more information has now come to light regarding Frazee's ex-mistress, Krystal Lee.

According to CBS News, the former rodeo queen and nurse has now shared her side of the story with authorities, including what she believes was the alleged motive and method of killing Berreth.

As stated by Lee, Frazee reportedly asked her to kill the young mother on multiple occasions. Each time he suggested doing it with a different method, including poisoning her with a caramel macchiato from Starbucks. For her part, Lee said she was unable to go through with it each time, which led to Frazee himself allegedly murdering Berreth with a baseball bat.

READ: Kelsey Berreth Update: Patrick Frazee Requests Evidence Suppression, Introduction Of Alternate Suspect

After Berreth was reported missing, police immediately begin questioning Frazee. At that time, he informed them that it was Berreth who had stated she wanted to end their relationship the day before Thanksgiving. Per his account, they then began discussing custody of their daughter Kaylee and came to an agreement that 50-50 custody was the best option. Additionally, Frazee said that he had seen her on Thanksgiving Day, but that it was just to exchange the baby and return her belongings.

Eventually, police searched Berreth's home where they were able to detect the presence of blood with the use of specific chemicals. They also found evidence of human decomposition through the assistance of cadaver dogs.

Lee's best friend, Michelle Stein, recently shared with "48 Hours" that the rodeo queen had revealed to her a month before Berreth disappeared that Frazee wanted to kill the mother of his child.

"She was very, very upset, very distraught. ...She had told me... that he had asked her to 'Take care of his baby mama,'" Stein said. Lee also told her friend that Frazee allegedly wanted to kill Berreth due to a potential custody issue pertaining to the daughter they shared.

Even though Lee has remained steadfast in the fact that she did not commit the crime, she has confirmed that she assisted Frazee in cleaning up the murder scene. Due to her account being the main source of information that investigators have right now, CBS News correspondent Nikki Battiste stated that Lee is the "bread and butter to this case" as she is "the only person in the world that they possibly have to convict Patrick Frazee."

As for why Lee didn't immediately come forward once news of Berreth's disappearance broke, her friend shared that it was because she had a "legitimate fear for her life."

"He did a lot of threatening. He threatened Krystal a lot. He threatened Krystal's daughter," she said, adding, "... He did say, 'Little girls come up missing all the time.'"

As of right now, prosecutors are seemingly counting on Lee's story to convict Frazee of Berreth's murder. He currently remains under tight security, while his 2-year-old daughter is being raised by Berreth's parents. His trial is scheduled to begin on Oct. 28.

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Gloria Williams was is facing three charges in relation to abandoning her three children in an apartment where their deceased brother's remains were kept. In photo: a crime scene tape blocks access to the public on March 20, 2018, in Sunset Valley, Texas. Scott Olson/Getty Images