A 20-year-old man is in critical condition after an interaction with police Sunday afternoon on the roof of an Etobicoke apartment building, from which the man fell.

Ontario's Special Investigations Unit is trying to determine what happened leading up to the man's injuries. So far, the SIU has released that police were called to the apartment building at about 1:45 p.m. and shortly after the tactical Emergency Task Force unit was sent there.

Toronto police Constable Tony Vella said officers responded to the apartment after a call came in for "unknown trouble."

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Officers made their way to the roof of the six-storey building and talked to the 20-year-old man, the SIU said in a statement, and at some point it appears the man jumped or fell from the building.

He was rushed to Sunnybrook Health Sciences Centre and was in critical condition as of Monday morning, an SIU spokeswoman said. The SIU, which investigates whenever there is a report of death, serious injury or allegations of sexual assault involving the police, has assigned six investigators and two forensic investigators to probe what happened.

Sunday's incident is the third time someone has fallen from an apartment building while Toronto police were present during the past two weeks.

On Friday, a Toronto man died after falling from the 15th floor of an apartment building near Queen and Parliament Streets. Another man died in late December after attempting to climb from one balcony to another on the 21st floor of an apartment building in Scarborough. The SIU is investigating those incidents as well.