Charles Henry Desjarlais, a 52-year-old Alberta man from Lethbridge, has been charged in connection with a sexual assault that happened in Calgary 20 years ago.

A 16-year-old girl was walking home from a school function in the city's northeast in late March 1995 when she was approached by a man, police say.

It's alleged the man forced her into an alley in Huntington Hills and sexually assaulted her.

The case went cold, but investigators re-examined DNA evidence six years later when the National DNA Data Bank was created.

"No DNA matches were found at the time; however, police resubmitted samples in November 2014 and a match was found," police said in a release.

Calgary police say the reason the DNA was resubmitted last year was because they hired an officer solely dedicated to investigating hundreds of sex crime cold cases.

Lengthy criminal history

The Calgary police encourage anyone with information about sexual assaults or other serious crimes to come forward "no matter how long ago the crime occurred."

"This case is a great example of the fact that we do not consider cases to be closed until they are solved," said Staff Sgt. Bev Voros.

"The cold case unit constantly re-evaluates cold cases to see if new technologies or information can help move old investigations forward and and there is no time limit on how long after and offense that we can lay charges."

After a nine-month investigation, the suspect was arrested without incident on Aug.15.

"With a cold case, you have to rebuild the entire file. A lot of stuff is on microfiche," said Voros. "You have to go back and talk with old investigators, maybe retired. Pull their notes. Pull the investigation. Make sure you talk to the lab and everything is in place. So, it's a lot of collecting old dusty files to put it together."

Desjarlais faces one count of sexual assault with a weapon.

He has a lengthy criminal history, including a sexual assault conviction in 1994 and a death threat conviction in 2002.