The sound of drums and calls of "Justice for Sean" filled the air outside the Winnipeg police headquarters Friday as dozens protested and called for answers about what happened to Sean Thompson, a father of three who died last month as he was taken into custody by police.

"I just want to know what happened," said his sister, Erica Thompson. "My brother was a good guy."

About 80 people joined her and other family members at the protest. Indigenous members of the community sang outside the building on Smith Street, repeating calls for body cameras to be worn by Winnipeg officers.

Very few details have been released publicly about the death.

Police were called to a home on Alfred Avenue at about 2:30 a.m. CT on June 26 after reports of a break-in.

They arrived and a man — now known to have been 30-year-old Sean Thompson — fled the area. He was found nearby on Burrows Avenue a short time later and as he was taken into custody, appeared to be in medical distress, according to a release by the Independent Investigation Unit (IIU).

The police watchdog said emergency crews arrived and rushed him to St. Boniface Hospital, where he was pronounced dead. The IIU did not release his name. He was identified to the media on Friday by his sister Erica.

She said the family wasn't notified until 30 hours after he died.

The IIU, which investigates all incidents involving police in which people are injured or killed, has taken over the case. It has enlisted a civilian monitor through the Manitoba Police Commission for help because it involves a fatality.

About 80 people gather outside Winnipeg police headquarters on Friday to protest. (Bryce Hoye/CBC)

'Kind-hearted kid'

Cheyanne Pruden said her cousin's sudden death has shocked the family.

"This wasn't supposed to happen," Pruden told CBC News at the protest. "I want the truth, that's why we're here."

Erica said Sean had some prior run-ins with law enforcement, but "was a kind-hearted kid, you know, he was a family guy," she said. He leaves behind a young son, daughter and step-daughter, she said.

Thompson, 30, died June 26 after an encounter with Winnipeg police, though the Independent Investigation Unit hasn't released many details about what happened. (Submitted by Felix Thompson)

Felix Thompson said he last saw his older brother about 24 hours before he died.

"He told me that he loved me," Felix said through tears. "I never knew that was the last time I'd see my big brother."

Sean was a hard worker who was employed in construction for most of his adult life, said Felix.

Felix Thompson, in the red shirt, hugs a friend at the protest. (Bryce Hoye/CBC)

'It doesn't make sense'

He said he's struggling to understand how his brother, who appeared healthy in the days before the incident, could just die.

"It doesn't make sense," he said. "This is about getting justice for my brother, for holding the police accountable."

The family is originally from Little Saskatchewan First Nation, and many including Sean were displaced in 2011 when a flood forced evacuations of four First Nation communities in the Interlake, said Erica.

They also have connections to Pinaymootang First Nation (also known as Fairford), where Sean was buried on Thursday near his father's grave, Erica said.

People gather outside Winnipeg police headquarters on Friday. The province's Independent Investigation Unit is looking into the case. (Bryce Hoye/CBC)

Erica said she noticed bruising all over her brother's arms and wrists at a funeral service in Winnipeg on Tuesday. The family is frustrated with how little detail they've been provided, she said.

"They're just saying my brother collapsed," she said. "Something happened."

The IIU has told the family they can't provide any other details as the investigation is ongoing, said Erica.

CBC News requested a response from Winnipeg police but has not heard back. Police don't typically comment on cases once they've been taken over by the IIU.