Patrick Frazee, the fiancé of the Colorado woman who went missing around Thanksgiving in December, had been planning to kill Kelsey Berreth for close to three months, court documents filed Monday revealed. The news comes as prosecutors came up with two theories regarding the death of 29-year-old.

Frazee, who was charged on five counts of murder relating to her death, including two counts of first-degree murder and three counts of solicitation to commit first-degree murder, had been working on a murder plot just a few months after Berreth purchased a home in Woodland Park for her and infant daughter Kaylee. According to the Daily Mail, Berreth spent $184,900 on a two-bedroom property about 15 miles away from the ranch where Frazee lived with his mother.

A family member claimed that just before her disappearance Berreth had split with Frazee, with whom she had Kaylee. However, this was never confirmed by investigators.

On Monday, Daily Mail reported that one of the two theories is that, Berreth was killed as a result of a robbery. The prosecution requested the court that Frazee's arrest warrant remains sealed, noting that publication of the details  could "seriously jeopardize the physical safety of potential witnesses in this investigation."

Court records indicate that Frazee will fight the charge of first-degree murder as he has requested that all evidence be given to his lawyers and even filed a motion for - limit pretrial publicity.

Berreth was last seen on Thanksgiving Day with her daughter at a Safeway in Woodland Park, Colorado. Three days after Thanksgiving Day, Berreth’s cell phone pinged near Gooding, Idaho, just 40 miles from Twin Falls. Police believe that the mother of one year old Kaylee is dead, however, her body or remains are yet to be found.

Last week, a judge granted physical custody of Berreth’s one-year-old daughter to her maternal grandparents. However, court records filed after the hearing also revealed that a custody battle could be brewing, between the two families.

"Paternal grandmother file a motion to intervene. The parties agreed to reserve for later hearing, paternal grandmother’s motion to intervene and placement request," read a summary of the hearing. "The court continued the grant of temporary custody of the minor child with maternal grandparents." 

Berreth's parents have been in acute grief and "absolutely devastated" after learning that their daughter might have been killed. Her cousin Jodi Garretson told Inside Edition: "I can't even fully comprehend how horrible they have to be feeling. That's their only daughter.”