A man has been arrested 16 years after a Toronto sex worker was sexually assaulted in an alleyway off Queen Street.

Last week, police issued a warrant for a suspect in a 1998 cold case, who turned himself into police on Thursday. The man was arrested and charged with sexual assault, robbery and failure to comply with probation.

Toronto police said a 33-year-old woman reported that she was assaulted and robbed on June 28, 1998.

She said been approached by a man at approximately 7:30 a.m., at Queen Street West and Beaconsfield Avenue, just east of Dufferin Street. The man took her to the rear of a building and assaulted her before taking her money and fleeing the scene on a mountain bike.

The woman and two of her friends chased him, but lost sight of him in the College Street and Roxton Road area. Police were called and investigated, but the perpetrator was never identified.

In August 2014, police were conducting a cold case investigation and re-tested the forensic evidence they'd gathered.

Toronto Police Det. Ali Ansari wouldn't provide details on the evidence collected, saying that the case was before the courts, but told media that a suspect was identified as a 56-year-old Toronto man.

"We don't forget these cold cases, and we will investigate them to the best of our abilities, hoping for a positive conclusion, no matter how long it takes," Ansari said at a news conference on Friday morning.