The aunt of a Massachusetts high school math teacher who was raped and murdered by one of her students in 2013 urged a judge on Friday to sentence the teenager killer to life in prison.

Prosecutors have asked Essex County Superior Court Judge David Lowy to sentence 17-year-old Philip Chism to 50 years in state prison for the murder of 24-year-old Colleen Ritzer, whose body was found dumped behind Danvers High School. State law would allow a life sentence, though Chism's young age would give him a chance at parole.

Chism was a 14-year-old freshman who had just moved from Tennessee when he killed Ritzer, cutting her throat with a boxcutter and using a recycling bin to dump her body.

"We've all been sentenced to a lifetime of pain, suffering and loss," said Ritzer's aunt, Susan Craig, the first of nine relatives and friends of the victim due to speak before Chism is sentenced. "This criminal deserves the same."

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In a court filing on Thursday, prosecutors asked Lowy to sentence Chism to 25 years for murder, with a subsequent 25-year sentence for rape. That would leave him in prison until the age of 64.

Chism's mother expressed sympathy for the Ritzer family, in a statement to reporters before the hearing.

"Words can't express the amount of pain and sorrow theses past two and a half years have been," Diana Chism said. "There is no one who has suffered more than the Ritzer family." 

Hours after murdering Ritzer, who had stayed late to provide students with extra help, Chism was found wandering along a state highway carrying a bag that contained Ritzer's identification and the box cutter he had used.

During the trial that ended in Chism's conviction in December, defense attorneys did not deny that Chism had carried out the attack, but contended he was not criminally responsible for his actions due to a long-undiagnosed severe mental illness that was aggravated by the move.

The trial was occasionally delayed by Chism, who was once observed beating his head on a floor and at another point refused to return to the courtroom after a break, telling his lawyer he was "about to explode."

Defense witnesses described Chism as a quiet and talented soccer player who was under emotional strain after relocating with his mother following his parents' divorce.

The jury found him guilty after nine hours of deliberations at a courthouse in Salem, Massachusetts.