The sex offender who strangled Surrey, B.C. teenager Serena Vermeersch to death has been sentenced to life in prison with no chance of parole for 17 years. 

Raymond Caissie, a 46-year-old criminal who spent most of his adult behind bars, attacked Vermeersch while she was walking home in September 2014.

The 17-year-old bravely fought back, but was ultimately overpowered and murdered at Caissie's hands.

At a sentencing hearing in New Westminster court Friday, the judge described the convict as a "violent, merciless man without a conscience."

"His background is abysmal. He has never been a productive member of society," Justice Gregory Bowden said.

The only mitigating factor in Caissie's sentencing is the fact that he pleaded guilty, Bowden added, which spared Vermeersch's family the stress of a trial.

The court heard the deadly attack, which was committed on a Monday evening, was a crime of opportunity. Caissie followed Vermeersch as she exited a city bus then forced her into a secluded area near the railway tracks in Newton.

Before she was killed, Vermeersch managed to slash at Caissie with an Exacto knife that she carried around in her purse for protection.

The judge said Caissie hit the knife out of her hand choked her until she was unconscious.

"He decided to kill Serena so that she could not tell anyone what had happened. He tied a piece of his T-shirt tightly around her neck and left," Bowden said.

Vermeersch died of asphyxiation.

Caissie, whose many convictions include sexual assault with a weapon, forcible confinement, robbery and theft, was last released from prison in 2013, about 18 months before the murder.

He was the subject of a police warning that cautioned he is known to offend "both violently and sexually, in both and opportunistic and impulsive manner."

The Crown and defence in his case both agreed that 17 years without parole is appropriate for someone with Caissie's background.

"It's a fair sentence," the convict's lawyer, Troy Anderson, said outside court. "The judge said based on his background it's unlikely he'll ever get parole,"

Anderson would not say whether Caissie has expressed any remorse for his crime, but pointed to his client's decision to plead guilty to second-degree murder.

"I think that's the strongest indication of remorse that you can have," he said.

With files from CTV Vancouver's Nafeesa Karim