A serial rapist who was described by one of his victims as "the monster under your bed" has been sentenced to 10 years in prison and was designated a long-term offender by a Calgary judge on Friday.

Charles Henry Desjarlais, 55, pleaded guilty last year to sexual assault for raping a 19-year-old woman in an alley in 1997. He has been raping women for at least 36 years.

It wasn't until he was behind bars for another historical "stranger rape" that Desjarlais called RCMP to provide a confession to the 1997 attack.

Desjarlais's first rape conviction came in 1982 and he was sentenced to 10 years in prison.

He was convicted of other sexual assaults that took place in 1994 and 1995.

On Friday, provincial court Judge John Bascom agreed with the joint submission from Crown and defence and sentenced Desjarlais, not only to another decade in prison, but once he's released, the sexual predator will be under supervision within the community for 10 years.

A sample of his DNA will be submitted to the national criminal databank.

"The recommended 10-year sentence is just and appropriate," the judge said. "I also find there is a substantial risk that Mr. Desjarlais will reoffend."

Desjarlais, who was in the prisoner's box wearing a blue prison jumpsuit, showed no emotion during the sentencing.

"It is clear the actions of Mr. Desjarlais​ negatively impacted the victim," Bascom said. "[It] haunts her daily life even 20 years after it happened. "

'Thinking I was pregnant at 9 years old'

As part of the long-term offender sentencing hearing, several of Desjarlais's victims wrote statements about how his crimes affected them.

"This man is a monster — the monster under your bed or in your closet," wrote one of Desjarlais's victims.

All of the women's identities are protected by a publication ban.

"One of the biggest emotional scars was thinking I was pregnant at nine years old," wrote another victim.

Originally, prosecutor Karuna Ramakrishnan was considering applying to have Desjarlais designated as a dangerous offender, which could have meant he would face an indefinite prison sentence.

Instead, Ramakrishnan and defence lawyer Mitch Stephensen put forward a joint recommendation for Desjarlais to be considered a long-term offender, which comes with the 10-year community supervision order.

'He had me by my hair'

Desjarlais's victims described various effects of the trauma they suffered, from PTSD to suicidal thoughts.

"I see him coming, I smell how dirty he was, I feel my hair being ripped out at the back. He had me by my hair and left a bald patch," said his 1994 victim.

She wrote that even though she was "loathed" to come forward to police after her attack, she felt she needed to in hopes other women wouldn't face the same terrifying violence.

"This offender LIKES to rape, he was a practised rapist when he grabbed me."

"He must not damage any more people. I came forward because I knew in June of 1994 that he had raped before and he would rape again."