TORONTO -- Nighisti Semret was walking home from work on a rainy morning in late October when a man police believe she didn't know stabbed her to death.

The details of the attack in downtown Toronto are gruesome -- her attacker plunged a knife through her body and hit her spine, his DNA was found under her fingernails, indicating a struggle, and in a new piece of information released Monday, police now think the suspect wounded himself during the attack.

Forensic teams have determined that the attacker -- who was using a kitchen-style knife with a 20-centimetre blade -- sustained a bloody wound during the tussle, likely to his hand or arm.

Toronto police are now asking the public to help them find the attacker, whose blood was found splattered on Semret's umbrella and on a bag she was carrying.

"There's blood coming off the offender's hand and it's cascading onto the umbrella in this particular case," said Det.-Sgt. Gary Giroux.

A $50,000 reward was also announced Monday for information leading to the attacker's arrest and conviction.

"I suspect, that unless it was a horrendous injury that he did not seek medical attention for this injury," said Giroux. "Somebody in the community may be aware of somebody who was tending to a hand or arm wound that didn't seek any treatment."

The attack took place in the early hours of Oct. 23, 2012, when 55-year-old Semret, who was a refugee from North Africa, was walking home from her job as a cleaning supervisor at a downtown hotel.

The mother of three was stabbed multiple times in a laneway in the Cabbagetown neighbourhood, where police are focusing their search for her attacker.

"I think it's just a unique part of the city and as a result of that the offender has, I believe, a connection to that particular area," said Giroux.

"He either lives in that area, frequents that area, frequents one of the shelters or hostels or soup kitchens or social assistances that are available in that area."

Police said several witnesses came forward after the attack, including a man who confronted the assailant but was unable to stop him from fleeing.

Investigators also posted surveillance video from a nearby building on YouTube which they said showed Semret being closely followed by the male suspect just prior to her death.

Police have already taken DNA samples from some individuals who were previously pointed out as potential suspects but have been unable to find a match so far.

While a motive for the attack is still unclear, police said Monday that the suspect's blood being found at the opening of Semret's bag might indicate a robbery.

"Based on the fact that the offender took some interest in relation to the bag that Ms. Semret was carrying, in relation to opening it, I'm going to suggest that robbery could be a very strong possibility," said Giroux.

The suspect is described as a white male, about five-foot-10 to six-foot-two, 150 to 200 pounds, with a medium build. Police say he was wearing a dark coat, a light-coloured scarf and a dark hat.