A Colorado man accused of murdering his fiancée last Thanksgiving relied on help from his secret girlfriend and spent months scheming about how to carry out the deed, prosecutors alleged in court Friday.

Patrick Frazee, 33, has pleaded not guilty to several charges, including first-degree murder, in connection with the death of 29-year-old Kelsey Berreth, who was last seen publicly in a grocery store with her 1-year-old daughter on Thanksgiving Day 2018. The cattle rancher’s fate is now in the hands of 12 jurors in a high-profile trial that could last as long as three weeks, according to lawyers.

Family members, supporters, and curious civilians packed the century-old Teller County courthouse on Friday for what has been deemed by local media as the “trial of the century.” Dressed in a blue-and-white striped shirt, Frazee sat emotionless in between his lawyers.

In their opening statement, prosecutors argued Frazee persuaded his secret girlfriend, Krystal Lee Kenney, to help him kill Berreth, then, after she failed to go through with the plans, fatally beat his would-be wife to death with a baseball bat on Nov. 22, 2018. Frazee then allegedly buried Berreth’s body and the murder weapon, which have yet to be found, at his ranch.

Prosecutors argued in court Friday that Frazee actually planned to murder his fiancé for two months—resulting in three unsuccessful attempts to kill her. Kenney told authorities some of the schemes included a poisoned Starbucks caramel macchiato, a metal pipe, and a baseball bat, according to her criminal affidavit.

All of those attempts were not successful, Kenney said, because she pulled out at the last minute.

“This is the face of a cold, calculating manipulator!” prosecutor Jennifer Viehman said in her opening statements.

Kenney, a nurse from Idaho, denied participating in Berreth’s murder but admitted to helping Frazee clean up the crime scene and is expected to testify against him in accordance with her plea agreement. She faces up to three years in prison.

On Friday, Frazee’s defense lawyers claimed the case has “foundational issues,” insisting that it was actually Kenney who murdered Berreth and then “lied” to authorities.

“What you have not heard is the raw and unedited version,” Ashley Porter, one of Frazee’s lawyers, said in her opening statements. “It looks good from the outside. It looks like it’s all there. But when you really start hearing the evidence and hearing the facts, you are going to realize deep foundational issues with this case.”

Berreth, a flight instructor at Doss Aviation, was last seen on Nov. 22, 2018, at a Safeway grocery store in Woodland Park, Colorado, pushing a shopping cart with her 1-year-old, Kaylee, according to security footage.

Ten days later, Berreth’s mother, Cheryl, reported her missing to authorities when she grew concerned after not hearing from her daughter. In her Dec. 2 statement, Cheryl said that Frazee told her he hadn’t spoken to his fiancée in days.

In court Friday, Cheryl testified she spoke to Frazee that day, choking up while discussing her daughter's last days.

“I said something along the lines of ‘Happy Thanksgiving. I hope you’re feeling better.' He said, 'Happy thanksgiving to you, too,'” she said, while dabbing her eyes with a tissue.

Frazee told cops he last saw Berreth the same day she was caught on camera at the supermarket, when she dropped off their daughter at his home. He told police he received a text from her three days later.

Authorities say Doss Aviation received a text from Berreth’s number on Nov. 25, stating that she would be taking the following week off from work without further explanation. That same day, her cell phone pinged off a cell tower in Gooding, Idaho—nearly 800 miles away from the missing mom’s home in Woodland Park, police said.

Frazee, who lived on a 35-acre ranch with his mother, was arrested and charged with his fiancée’s murder on Dec. 21. Woodland Park Police Chief Miles De Young said at the time that authorities believed Franzee murdered Berreth at her house.

On Nov. 22, Frazee allegedly told Kenney he took matters into his own hands and killed his fiancée with a baseball bat after convincing her to put on a blindfold for a “candle smell test,” prosecutors said. Their toddler was allegedly laying down in a nearby room during the slaying.

Kenney said she was so afraid of Frazee that she agreed to help clean up the murder scene at Berreth’s house, and watched him as he burned the body and the baseball bat somewhere on his Florrisant ranch.

The nurse pleaded guilty in February to evidence tampering for her help disposing of Berreth’s cell phone in Idaho to trick authorities at Frazee’s behest. Prosecutors on Friday alluded to Lee’s cell-phone trail and her witness testimony as key evidence showing Frazee killed his fiancée with her help.