BOISE -- The man who murdered an 18-year-old Boise State student last fall will never leave prison again, a judge ruled Wednesday, in what he described as a fitting end for a felon whose life was marked by countless acts of violence and sexual aggression.

"Mr. Marchant is a dangerous person," Judge Jonathan Medema said. "Mr. Marchant has been dangerous for a very long time, and I have confidence that he will continue to be dangerous until the day he dies."

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Bruce Marchant, 62, admitted in September to attacking Sierra Bush in her bedroom while her father was attending church, candidly explaining to the judge that he strangled her to silence her screaming. Marchant, a multiple-time felon, had been evicted as a tenant by Bush's father not long before the murder.

Bush's naked body was found in Mores Creek near Idaho City nearly a month later.

Bush's mother Mary Helen Green said after her daughter's disappearance, she had held out hope that Bush was simply being held captive somewhere. Each time she received a phone call from detectives or heard the sound of a helicopter or siren, her heart lifted with the thought that her daughter was being returned to her.

Green described her grief as a "boulder" she carried with her everywhere.

"I loved this child," she said, as she began to cry. "Being her mother was one of the best things I have ever done."

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Bush's mother and stepfather described the victim as a kind, artistic teenager who loved skiing, writing stories and creating costumes to wear to cosplay conventions. Bush - who had recently began going by the name Simon to some of her friends - was thrilled at her acceptance to Boise State and was looking forward eagerly to her future, her family said.

Bart Green said Marchant had robbed his stepdaughter of the chance to graduate college, find a career, fall in love, or realize the potential that had been waiting for her in adulthood. He told the judge he was "haunted" by thoughts of Bush's terrified final moments.

"I will forever have to contemplate what brutality Mr. Marchant inflicted on Sierra prior to killing her, and the absolute fear, terror, and pain she must have experienced," he said.

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Prosecutor Brian Naugle said Marchant should never get another chance to leave prison and hurt anyone else, arguing that the cruelty of the attack called for the harshest possible sentence.

"To choke the life out of a perfectly innocent person for crying out for help because you've broken into their house and raped them exhibits a level of depravity that is thankfully rare," he said.

Marchant was originally charged with rape and kidnapping in addition to first-degree murder in Bush's case; those charges were later dropped as part of a plea deal.

The killer was arrested at a Veterans Affairs hospital in New York months after Bush's body was discovered. Although he had quickly emerged as a person of interest in the teen's disappearance, he had left town after speaking with detectives.

Naugle said investigators found a story handwritten by Bush inside Marchant's car, along with a pair of men's gloves stained with blood that was later determined to be the victim's.

The murder was "the kind of thing that our nightmares are made of," Naugle said, but noted Bush's death was not Marchant's first violent act.

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In his 20's, Marchant set fire to his trailer with his wife and young daughter inside "in an apparent attempt to kill them," the prosecutor said. Both survived, and Marchant somehow escaped a long prison sentence. Later, he robbed a post office at gunpoint.

After being paroled in that robbery, he absconded from parole and headed to Kootenai County to commit another robbery, this time firing a shotgun at Idaho State Police troopers who tried to stop him.

The troopers returned fire, hitting Marchant in the face. He was ultimately sentenced to 20 years in prison, in addition to the remainder of his federal sentence in the earlier robbery.

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Even inside prison, Marchant acted out violently and sexually, attacking inmates and staff and refusing to follow prison rules, Naugle said.

After his release in 2008, Marchant was frequently accused of making crude comments and
inappropriately touching women, even bragging about sexual assaults, the prosecution said.

"It is the state's belief that if Mr. Marchant was ever released from prison, he would commit another violent crime," Naugle said.

But defense attorney Nicole Owens asked for a sentence of 20-to-life, allowing Marchant another chance at parole at the age of 82. She noted that the defendant had been diagnosed with mental health issues including bipolar disorder and schizoaffective disorder, but could control his behavior when properly medicated.

In a statement before the sentence was handed down, Marchant told the judge he had been in "a manic phase" and sleeping just a few hours a night when the murder occurred.

"I'm sorry, real sorry, for these people that have lost their daughter," he said. "There's no replacing any of that. That's all I have to say."

Medema was not impressed.

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Some defendants that come before the judge leave him struggling to determine a fair sentence - one that is neither too, harsh, nor to light, he said. Marchant wasn't one of them.

"My primary obligation is simply to protect the community from Mr. Marchant doing something
like this in the future," he said. "It would be a dereliction of my duty to fashion a sentence that ever permits you to be released into society again."

Marchant sat stock-still as the judge handed down the sentence. Medema saved his final words
for Bush's family, telling her mother and stepfather he hoped their sorrow will not keep them from pursuing the activities and traditions they once relished doing with Bush.

"In my view, he's taken enough from you," the judge said of Marchant. "He doesn't deserve the right to affect your lives in the future."