DENVER -- The 22-year-old former security guard accused of posing as a police officer to kidnap and kill University of Northern Colorado student Lacy Miller will now spend the rest of his life in prison.

Jason Peder Clausen pleaded guilty Thursday to first-degree murder with the agreement that the other kidnapping charges be dropped and that he would not face the death penalty, 7NEWS reported.

Clausen was sentenced to life in prison without possibility of parole.

During Thursday's hearing the district attorney said that the murder was "sexually motivated."

With Clausen's guilty plea came the release of numerous police records. The autopsy report from the Colorado Bureau of Investigation showed that the 20-year-old woman died from multiple trauma to the head, neck and chest. There was also significant postmortem tearing in her rectum and possible pubic hair and fluid on her buttocks, the report said.

According to the search warrant affidavit for Clausen's home, a disposable camera was found in his room. The developed film showed that he took photos of Miller on his bed. The report did not say whether she was still alive at that time.

Video

Laci Miller's Family Express Relief, Sorrow

Prosecutors said that Clausen drugged the UNC sophomore, beat her to death and kept her body in a storage shed before he dumped her in a canyon northwest of Fort Collins. He also apparently tried to use gasoline to set her body on fire before wrapping it in plastic and duct tape and burying her. It was not known how badly Miller was burned when authorities discovered her body about a week after her disappearance, 7NEWS reported.

Police said Clausen also apparently showed her body to his roommate about 26 hours after her death. He had also asked another friend to dispose of her purse even though it still had her identification inside, 7NEWS reported.

Miller, 20, was last seen on the early morning of Jan. 18. She had just dropped off a friend and was driving to her parents' Fort Collins home. Her mother and stepfather reported her missing after they found her black Mitsubishi Mirage locked and parked on the street two doors away from their home. Family members said that this was odd because she only parked on the driveway or in the garage.

Investigators were led to Clausen after his roommate told police that Clausen showed off Miller's tarp-wrapped body inside his truck.

Miller's body was found Jan. 26 in the Cache La Poudre Canyon.

Clausen, a former Fort Collins Police Explorer Scout, was known to drive around in his white Ford Expedition with red and blue flashing lights and "act like a cop," according to sheriff's records. Records confirm that he had law-enforcement training and tools, including at least four guns, handcuffs, a bail bondsman's badge and a police light installed on the dashboard of his white sports utility vehicle.

In court Thursday, Miller's mother, Wendy Cohen, talked about the joys of having a child and how much she will miss her daughter.

"There isn't justice for a lost life. Justice means fairness and there's no fairness in this because she's dead. She's gone. And I trust someday that he will have to face God for it," Cohen said.

She said was glad that she had an opportunity to speak about her loss in front of Clausen and his family and relieved that she wouldn't have to hear the details of Lacy's brutal death over and over during a long trial process.

"I recognized that ... he owned (up to) what he did and he didn't have to do that. So, I'm just glad it's over," Cohen said. "I'm glad that we can all be done and move on ... It's a relief to know that I don't have to keep doing this, now I can heal."

She said that she also tried to console the family of her daughter's murderer.

"I just told his mother that I was sorry and I thanked her. And I told her that we would get through this somehow and that I loved them. It's a bad situation," Cohen said amidst tears.

Clausen's parents didn't speak to reporters but released a statement through their lawyer. The statement said, in part, "Nothing we can say to the Miller and Cohen families can lessen the heartache which they feel over the loss of Lacy. Nor do we pretend that there is not a large void in the lives of Lacy's family and friends ... Our purpose is not to mitigate Jason's actions but to recognize that two families have been devastated. We still have our son and brother and this is not lost on us. Our family believes in justice, and believe that justice has been served."

Clausen didn't make a statement but his lawyer, Andy Gavaldon, said the fact that he made a guilty plea shows that he deeply regrets his actions.

Clausen remains in custody at the Larimer County Detention Center.