Toronto police say the man who likely attacked and killed Nighisti Semret last October left behind blood DNA evidence and may have even wounded himself during the attack.

Semret died when she was stabbed from behind on Oct. 23, 2012, while walking home from work at around 7 a.m.

Semret, 55, had just finished a night shift as a supervisor of a cleaning crew at the Delta Chelsea Hotel. Security video from the area released by Toronto police shows her walking down a laneway connecting Bleecker Street to Ontario Street prior to the attack.

On Monday Det. Sgt. Gary Giroux held a news conference to update reporters about the case. He said a DNA analysis of blood found at the scene and under Semret's right fingernail is a match, suggesting Semret scratched her attacker.

The attacker's blood was also found on a bag and on an umbrella that Semret was carrying.

Police say the knife used in the attack was large (at least 20 cm long) and is likely a kitchen-style knife.

Giroux said some of the blood spilled at the scene belongs to the attacker, suggesting he may have stabbed himself during the attack, which happened on a dark, rainy morning. Giroux said the wound would likely be to the attacker's arm or hand.

"That wound may or may not have been medically treated," said Giroux.

Police also announced a $50,000 reward for any information that leads to a conviction in the case.

Anyone with information is asked to contact police at 416.808.7400. Tips can also be sent anonymously to Crime Stoppers at 416-222-TIPS (8477)