A 31-year-old Toronto man has been found guilty of four counts of first-degree murder in what one investigator has described as "irrational" and "cold-blooded" shootings.

Mark Moore, who is currently serving a 12-year sentence for his role in a violent 2010 jewelry store robbery, has been convicted in the murders of Jahmeel Spence, Courthney Facey, Mike James and Carl Cole, who were all shot to death between June and November 2010.

Speaking to reporters outside the Superior Court of Justice at 361 University Avenue Saturday evening, lead investigator Detective-Sergeant Hank Idsinga said there was a mix of tears and "jubilation" when the verdict came down.

"The crimes are completely senseless. He killed three victims who were absolutely unknown to him," Idsinga said.

The theory put forward by prosecutors, Idsinga said, was that Moore, an aspiring rapper, committed the murders simply to establish street credibility as a gangster.

"Some of his rap lyrics, which were introduced as evidence, talked about him being able to in his words, ‘shake the streets," he added.

"During a couple of the murders, it looks like that’s exactly what he was trying to do."

The murders were said to be carried out using the same two guns.

Moore, who is facing life in prison with no chance of parole for 25 years, will be sentenced on June 16.