Firefighters responded to a call at 5754 Yonge St. on the afternoon of July 13, 2013.
A woman's body was found after the fire was put out in one of the apartment units on the second floor.
Janina Wrigglesworth, 72, was pronounced dead at the scene. Her death was soon deemed a homicide.
Two days after her death, police released a photo of a man they were trying to identify.
On Wednesday, Toronto police Det.-Sgt. Terry Browne told reporters that the person in that photo is the person now facing a charge of first-degree murder.
Blake Anthony Wilson, 26, faces a single count of first-degree murder. He was due to appear in court on Wednesday.
The detective told reporters Wednesday that Wrigglesworth was involved in the sex trade and advertised in local publications.
Browne said it was "not uncommon" for potential clients to come over to her apartment.
Police want to hear from anyone who spoke to her on the phone in the week leading up to her death.
"Whether you did in fact attend her address or not, we need to hear from you because it’s part of our investigation," Browne said.
"And I can only reiterate: If you choose not to contact us, that’s your privilege or right, but we will be placing those calls to you."
Browne said that Wrigglesworth was living by "limited means," sending any extra money she had to family living overseas in Poland.
The detective said Wriggleswoth had retired from a "federal job" that provided her with pension payments. But she also did people's taxes and derived some income "from the sex-trade industry," Browne said.
Police say they are in possession of "numerous" tax returns that they would like to return to their owners. Anyone who would like to retrieve returns that had been left with Wrigglesworth can contact investigators at 416-808-7400 and make arrangements pick to them up.