Massachusetts teen awaits sentence for gruesome murder of teacher
Philip Chism, 14, stands during his arraignment for the death of Danvers High School teacher Colleen Ritzer in Salem District Court in Boston, Massachusetts October 23, 2013. (REUTERS/Patrick Whittemore/Pool)

A Massachusetts teenager found guilty of raping and murdering a math teacher at his suburban Boston high school in 2013 will learn on Friday how much of his life he will spend in state prison for his crimes.

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.

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 behind the school.

Despite his youth, he was tried as an adult, though Massachusetts laws do not allow him to be sentenced to life in prison without possibility of parole, the state's normal punishment for first-degree murder.

Prosecutors in a court filing on Thursday 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.

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.

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-un diagnosed 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.

(Reporting by Ted Siefer; Writing by Scott Malone; Editing by Alistair Bell)