A care agency in B.C.'s Fraser Valley has launched an internal investigation into the death of a 17-year-old Indigenous boy whose body was found in a group home last month.

The teenager, whose name has not been publicized, was in the care of the Fraser Valley Aboriginal Children and Family Services Society when he went missing on Sept. 14.

It wasn't until four days later that he was found hanging in his own bedroom closet, according to First Nations leaders who have demanded accountability for what happened.

On Thursday, the care agency issued a statement promising to investigate the circumstances surrounding the tragedy.

"We are heartbroken by the loss of this youth," it reads. "We trust that findings from an investigative review will give the grieving family and agency staff answers, comfort, and understanding."

Fraser Valley Aboriginal Children and Family Services Society also said it would be "full co-operating with all external investigations" into the tragedy. The statement included the names of Grand Chief Doug Kelly, president of the Stó:lō Tribal Council; Marion Mussel, president of the Xyólheméylh board of directors; and Chief David Jimmie, president of the Stó:lō Nation Chiefs Council.

"We are saddened, and on behalf of our agency we send love, prayers and condolences to the family, caregivers and the community," the statement reads. "We have called upon our Respected Elders to help us by sharing their traditional knowledge, and offering healing circles for the family and staff to get through this difficult time."

It's unclear whether any other investigations are being conducted, apart from the one underway at the BC Coroners Service, which investigates all deaths in the province that are unexpected, unnatural or unexplained.

Earlier this week, the Union of B.C. Indian Chiefs, First Nations Summit, B.C. Assembly of First Nations, and the Indigenous Bar Association of Canada shared troubling details about the teenager's death.

While the boy's disappearance was reported to the Abbotsford Police Department on Sept. 15, advocates say his body "had apparently been hanging there" in his closet the entire time people were searching for him.

"There obviously wasn’t a thorough enough search by staff of this home, nor by the police," said B.C. Assembly of First Nations Regional Chief Terry Teegee on Wednesday.

The groups have also charged that the teenager's death was declared a suicide too quickly, and that police were too quick to decide there were no grounds for further investigation. They said an autopsy was only ordered following pressure from First Nations leadership.

Lawyers for the boy's family have also argued the death should be independently investigated.

"I think it’s sadly an issue of racism," said Teegee. "It seems Indigenous people aren’t worthy of a thorough investigation."

Abbotsford police issued a statement to CTV News saying that "several officers completed multiple searches, day and night," until the teenager was found dead.

Authorities said the boy was known to police after being the subject of previous missing person reports, and that there had been "no indication that he was suicidal, or using drugs or alcohol" at the time of his latest disappearance.

With files from CTV News Vancouver's St. John Alexander