Det. Sgt. Steve Bereziuk said there was a relationship between the boy and the suspects, but he didn't know the extent of it.
She said her son, Devan Selvey, had been bullied at the school for quite sometime, but did not go into any further detail on the matter.
Speaking with CTV News Toronto off-camera one day after her teenage son had died, Shari-Ann Sullivan Selvey said she was alerted to Sir Winston Churchill Secondary School, located near Parkdale Avenue South and Main Street East, on Monday afternoon for a problem.
Police said they will be providing an update on the investigation at 4 p.m. ET.
"She's witnessed something awful here", Bereziuk said.
Police told reporters during a news conference at the scene Monday night that three suspects had been arrested and police are searching for two others, and that some of the suspects may have been students at the school.
There is a court-ordered publication ban on releasing the name of the adult male accused.
They have not offered a motive for the attack, but a fundraising page set up by someone claiming to be Devan's sister suggests he had been bullied. "She's devastated." he said. "He wanted to become a mechanic; he loved cars". "Even I did. I tried to save him and I couldn't".
Bereziuk said Devan's death has prompted widespread co-operation from the community, but has also shocked residents of the city west of Toronto. "It's hard to comprehend right now, to be honest with you". "I feel so, so bad for that family".
They are asking anyone with information or cellphone video to contact police at 905-546-4123 or to reach out to Crime Stoppers anonymously. Social media evidence will also be collected.