For more than a month, the police in Toronto have been trying to solve a mystery. They had a photograph of an unidentified dead man, and they had discovered human remains in planters where a man suspected of multiple killings had worked as a landscaper.

On Monday, the police announced that they had charged the suspect, Bruce McArthur, with first-degree murder in the death of an eighth alleged victim — Kirushna Kumar Kanagaratnam, the man in the photograph.

The development was weeks in the making. Investigators released Mr. Kanagaratnam’s photograph to the public on March 5, declining to say where it had come from and appealing for help identifying him. They enlisted the assistance of an officer who spoke Tamil, and coordinated with Mr. Kanagaratnam’s family, who was still in Sri Lanka.

“The stress and anxiety over dealing with hundreds of tips, hundreds of missing-persons occurrences and dozens of potential identifications for the eighth victim has been enormous,” Sgt. Hank Idsinga said at a news conference.