Life for US schoolboy Philip Chism who raped and killed teacher Colleen Ritzer

An American teenager who raped and murdered his maths teacher when he was aged just 14 has been sentenced to life in prison. In December, Philip Chism, who is now 17, was found guilty of killing of Colleen Ritzer, 24, at Danvers High School in Boston in 2013, after he followed her into a school bathroom, strangled her, stabbed her at least 16 times and raped her.

He will not be eligible for parole for 40 years.

Sentencing on Friday, Judge David Lowy described the murder as "brutal and senseless".

"Colleen Ritzer lived a life of quiet heroism," Lowy said. "The crashing waves of this tragedy will never wane."

Ritzer's family, however, told the press they were unhappy that Chism might eventually get out of prison.

"We are devastated and feel betrayed with Judge Lowy's inability to give three consecutive life sentences without the eligibility of parole to the individual that took [her] life in such a horrific manner," said her mother in a statement. "We are disgusted and personally offended with the defense's repulsive recommendation that Colleen's killer be parole eligible within 15 years, therefore putting him back into society at age 29 to kill again.

"The defense legal maneuvering is despicable and demonstrates utmost disrespect for our daughter and sister, Colleen's life. Evil cannot be rehabilitated."

Chilling CCTV footage seen by the jury showed Ritzer walking through the school's corridors to a bathroom. Chism is shown leaving a classroom and following her in. He is then caught wheeling her body through the school in a recycling bin, on his way to dump her remains in some nearby woods.

Chism was convicted as an adult, and was sentenced to 25 years to life in prison for murder, and 40 years each for aggravated rape and armed robbery. The sentences are to be served concurrently.