The remains of over 200 students were found on the grounds of a desolate former residential school for indigenous children in Canada.

The British Columbia First Nation Tk’emlups te Secwépemc confirmed the body parts belonged to students of the Kamloops Indian Residential School, The Vancouver Sun reports. They were found on the Kamloops reserve using ground-penetrating radar.

Canada’s Prime Minister Justin Trudeau tweeted his sentiments regarding the discovery on Friday (May 28). “The news that remains were found at the former Kamloops residential school breaks my heart – it is a painful reminder of that dark and shameful chapter of our country’s history. I am thinking about everyone affected by this distressing news. We are here for you,” he tweeted.

In a news release issued by Tk’emlups te Secwépemc, First Nation Chief Rosanne Casimir called the discovery an “unthinkable loss that was spoken about but never documented at the Kamloops Indian Residential School.”

Casimir believes the deaths are undocumented and that some of the children found were as young as three. “Given the size of the school, with up to 500 students registered and attending at any one time, we understand that this confirmed loss affects First Nations’ communities across British Columbia and beyond,” Casimir said in the release. “Access to the latest technology allows for a true accounting of the missing children and will hopefully bring some peace and closure to those lives lost.”

The chief said the efforts to identify the remains was led by the First Nation’s language and cultural department in addition to ceremonial knowledge keepers, who made sure everything was “in line with cultural protocols.

The Times Colonist, a daily news publication for the city of Victoria, BC reports the school was once the largest in Canada’s residential school system. The school closed in 1978, according to the Tk’emlúps te Secwépemc Nation.

According to Reuters, a 2015 investigation into Canada’s harsh residential school system found indigenous children were forcibly separated from their families amid a “cultural genocide.” The report highlighted horrific physical abuse the students endured such as rape, malnutrition and other harm. It found more than 4,100 children died while attending residential schools across the country, which were mostly run by Christian churches from the 1840s to the 1990s.