Calgary police have laid charges after using DNA evidence to identify the suspect in a Beltline sexual assault that happened 20 years ago.

Charges were laid against Charles Henry Desjarlais, 54, a repeat offender who is serving time for a similar crime.

Staff Sgt. Bruce Walker of the sex crimes unit said the victim has been informed of the charges. He said it is a comfort for her to know the case has been solved.

"She is doing as well as can be expected," Walker said Thursday at a news conference. "There is satisfaction that we can find closure for the victim."

Staff Sgt. Bruce Walker is in charge of the Calgary Police Service's sex crimes unit. (Justin Pennell/CBC)

The Beltline sexual assault happened around 5:30 a.m. on Aug. 14, 1997. A woman was walking along Eighth Street S.W. when a man approached her somewhere between 10th and 11th avenues.

He pulled the woman into the alley, threatened her and sexually assaulted her, police said. The perpetrator made the woman walk through alleyways with him before fleeing.

The case remained unsolved until recently, police said.

The breakthrough happened last November when Desjarlais, who was in custody, contacted the Innisfail RCMP to turn himself in for a sexual assault that happened sometime in the late 1990s.

The information was passed on to the Calgary Police Service. Detectives reviewed several unsolved cases from that period. DNA evidence led the investigators to lay charges against Desjarlais.

He has been charged with sexual assault, sexual assault with a weapon, uttering threats and kidnapping.

Last year he was sentenced to five years in prison on another cold case. Desjarlais was arrested two years ago when DNA evidence linked him to the assault of a 16-year-old Calgary girl who was on her way home from school in 1995.

His lengthy criminal history includes a sexual assault conviction in 1994 and a death threat conviction in 2002.

The sex crimes unit has three investigators dedicated to looking at cold case files. Walker said they have looked at Desjarlais in connection to other unsolved sex crimes in the 1990s but have not opened any new investigations.