Toronto police have arrested and charged a man with first degree murder after a woman died of an assault in a residential building in the Weston and Lawrence area.

Karl Hoyes, 49, has been charged in the death of Margaret Cameron, 66. He was scheduled to appear in court at Old City Hall on Saturday.

Police say Cameron, Toronto's 71st homicide victim of the year, was fatally assaulted in an elevator at 1765 Weston Rd., south of Lawrence Avenue West, on Friday night. Police were called to the address at about 6:45 p.m.

Det. Rob North, spokesperson for Toronto police's homicide squad, told reporters at police headquarters that the incident had a "sexual assault component" that detectives are continuing to investigate.

Officers arrested Hoyes without incident in the area of Peter Street and Queen Street West at about 12:20 a.m. on Saturday, police said in a news release.

"It's a completely unacceptable, tragic incident that happened here in the city," North said on Saturday.

North said police were able to make a quick arrest because they canvassed the building for surveillance video, reviewed footage from CCTV cameras and looked at images from different angles. Officers from the Gun and Gang Task Force and 51 Division's major crime unit helped officers from 12 Division to identify a suspect, he added.

Toronto police taped off part of this residential building at 1765 Weston Rd., south of Lawrence Avenue West, following the fatal assault. (CBC)

On Friday night, when police arrived at the building, they found the woman on an upper floor, suffering from "obvious head trauma."

Officers tried to save her life by performing CPR and paramedics took her to a trauma centre, where she died of her injuries, police said.

North said the assault happened as the elevator made its way to the upper floors of the building.

Suspect, victim not well known to each other

Police believe the suspect and victim may have known each other through a "loose circle" of friends. North said the victim lived in the building where the assault happened, while Hoyes was a former resident.

"They may have had some very minor interaction, but they were not well known to each other," North said.

Police are still trying to identify and locate witnesses. Anyone who was in the building at the time of the assault and who has any relevant information about the incident or the suspect is urged to come forward. (Michael Rich/CBC)

Cameron has family in the city and abroad and next of kin are being notified. "She has an extended family living outside of the country," he said.

According to North, Hoyes is known to police. North declined to say if a weapon was used in the assault. Police will look to see if Hoyes has any mental health issues, he said.

North said police believe the assault is an isolated incident and Hoyes is the only suspect.

"It is simply a residential highrise in the northwest portion of the city. There is another highrise directly across from it. It's no different from any other highrise in the city of Toronto," he said. "It's well lit. There is a lot of people walking around in the area and in the community."

North urged people to be aware of their surroundings at all times.

Police are still trying to identify and locate witnesses. Anyone who was in the building at the time of the assault and who has any relevant information about the incident or the suspect is urged to come forward.