Toronto police continued to look for the killer of Tyson Bailey on Monday while grief counsellors arrived at Central Technical School where the 15-year-old was a student and football player.

Bailey was shot several times inside a stairwell at a Regent Park apartment building Friday afternoon. He later died in hospital. He did not live in the building.

Det. Sgt. Justin Vander Heyden said police still have no idea why Bailey was killed. (CBC)

For hours Sunday, forensic investigators combed through a 13th-floor apartment in the building, removing several paper bags full of evidence, including cellphones, one of which belonged to Bailey, police said.

"The occupants of that apartment all came to 51 Division [police station], and were all interviewed that night, and the occupants were all co-operative," said Det. Sgt. Justin Vander Heyden.

Police have described one of the occupants of the apartment as "a person of interest." He was last seen walking down the hall with Bailey on Friday.

Police said the two ended up in the stairwell where Bailey was later found wounded and bleeding. He had been shot at least four times.

"I believe there's at least one other person involved that was in the stairwell," Vander Heyden said.

Memorial grows

'He never skipped — always in class, always trying to focus on school and sports.'—Jason McQuabbie

Outside the building, a make shift memorial continued to grow on Monday.

Bailey was well known in the Regent Park neighbourhood, and police still don't know why he was killed, or even why he was in the building.

Central Tech student Jahalya Benight first heard about Bailey's death on Facebook on Friday afternoon.

"And I was, like, I know that guy. He goes to my school, and then I was, like, oh my gosh, he was in my class," Benight said.

Like most students at the high school, Benight couldn't believe it.

"He was so nice, never mean to anybody. He would respect everybody — just the nicest guy," he said.

Bailey was in Grade 10, and was the junior football team's starting running back.

At the school Monday morning, the team's head coach fought back tears as he told reporters about his young player, and how he watched him mature as athlete and a person.

The Toronto District School Board has brought in a separate grief councillor just for the football players.

"He wanted to play football. He never skipped — always in class, always trying to focus on school and sports. [He] was never into the bad stuff," said Jason McQuabbie, who was also on the football team.