Results of an autopsy were unknown and family of the man, who had yet to be buried, were requesting privacy over the weekend, his lawyer said late Friday.
"It's obviously a big shock — he was a young man," Andrew Brouwer told The Canadian Press. "There's still a good deal of uncertainty about exactly what happened."
However, an activist group that works with detainees cited hospital staff and the family as saying the man died from a lack of effective medical care for his diabetic condition — although Brouwer did not confirm that.
The group, End Immigration Detention Network, accused Canada Border Services Agency of a lack of transparency and decried its use of prisons to hold foreigners not charged with any crime.
"CBSA is clearly unwilling to act on the death and misery caused by immigration detention," the network's Syed Hussan said in a statement. "It needs to end."
In a brief news release late Thursday, the border agency announced the death of the man in hospital in Peterborough, Ont.
"The Canada Border Services Agency was notified by the Peterborough General Hospital that an adult male detainee, who was receiving care, passed away in hospital," the statement said.
The release, issued about 18 hours after the death, gave no further information about who he was, where he was from, or any other circumstances of his detention or death.
A trickle of details emerged a few hours later when the province's Special Investigations Unit, which probes reports of death or serious injury involving police, said it was investigating.
The unit said the man was 39 years old and was being detained at the Central East Correctional Centre in Lindsay, Ont. He had been admitted to hospital for medical reasons under police escort, the SIU said.
"At approximately 1 a.m. on Thursday, June 11, 2015, the man became agitated," the SIU said.
"At the request of medical staff, he was restrained by the officers and by health professionals. Shortly after, the man went vital signs absent and was subsequently pronounced dead."
On Friday, a spokeswoman for the border agency would only confirm the already announced SIU investigation.
"We are not releasing any further information because the investigation is ongoing," Antonella Digirolamo said. "That's all I have for you."
Police referred inquiries to the SIU, which was similarly tight-lipped. However, spokeswoman Monica Hudon cited SIU policy of deferring to the wishes of family.
"The family has asked us not to release the name," Hudon said Friday.
Correctional Service Canada does release names of inmates who die in its custody. It's only in recent years that CBSA has begun to release some information — the date and place — about detainee deaths.
Coroner's juries have criticized the border agency in the past for how it dealt with detainees — especially in terms of providing medical authorities with proper health records.
End Immigration Network said this was the 12th reported death in detention custody and the second this year. It called on Ontario to sever its ties with CBSA.
The Canadian Red Cross has long criticized a lack of access to immigration detainees in Ontario jails but a spokesman for Ontario Correctional Services Minister Yasir Naqvi said Friday the organization can visit them — on request.
"We are currently finalizing an agreement that seeks to establish a formal arrangement between the ministry and the Red Cross to build on our current relationship and improve access," said spokeswoman Lauren Callighen.
Federal Public Safety Minister Steven Blaney refused to comment.
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