Montreal police are asking for the public's help in identifying a serial attacker who has been preying on women at least since 2006.  

Evidence has linked the same man to a string of attacks in north-end Ahuntsic-Cartierville as well as the neighbourhoods of Rosemont-La Petite-Patrie and Mercier-Hochelaga-Maisonneuve.  

Investigators are releasing three sketches of the attacker, one drawn from the recollection of witnesses in 2006 and the others after attacks last year.  

During most of the attacks, the woman was jumped from behind as she walked along the street during the evening or overnight hours.  The attacker would clamp his hand over the woman's mouth and sometimes threaten her with a knife.  

The suspect is described as a French-speaking white man about five-foot-nine and aged between 40 and 50, who sometimes wears glasses.