Leaders of a First Nation in Saskatchewan said Thursday that investigators have found 751 unmarked graves at the site of a former residential school—mere weeks after the discovery of the remains of 215 Indigenous children in British Columbia rocked Canada.

Chief Cadmusn Delmore of the Cowessess First Nation made the announcement at a press conference. He noted that the Catholic church that had been operating the residential school and overseeing its cemetery removed the headstones.

“This was a crime against humanity, an assault on First Nations,” said Chief Bobby Cameron of the Federation of Sovereign Indigenous First Nations in Saskatchewan. He added that he expects more graves to be discovered on residential school grounds across Canada.

“We will not stop until we find all the bodies.”

The bodies were unearthed at the Marieval Indian Residential School, which operated from 1899 to 1997 where Cowessess is now located, about 87 miles east of Regina, Saskatchewan’s capital.

It’s not clear how many of the remains found belong to children, Delorme said. “There are oral stories that there are adults in this gravesite, as well.”

Last month, the remains of 215 First Nations children were found buried on the site of what was once one of Canada’s largest residential schools in Kamloops, BC. Pope Francis expressed sorrow for the tragic discovery of the bodies, but stopped short of apologizing for the Catholic Church’s involvement in the residential school system.

“The Pope needs to apologize for what happened,” said Delmore.

“An apology is one stage in the way of a healing journey.”

In the weeks since the Kamloops discovery, a movement to cancel Canada Day has been gaining momentum across the country. Celebrations of the national holiday have been called off in Victoria, BC, Wilmot Township, Ontario, and several First Nations out of respect for the Indigenous community’s grief this year. 

Residential schools for Indigenous children existed in Canada from the 17th century until the late 1990s. It’s estimated that over 150,000 First Nations, Inuit, and Métis children were taken away from their families and forced to attend state-funded Christian schools in an effort to assimilate them into Canadian society. Students were punished for speaking their Indigenous languages or expressing their identities. The last school shut down just 25 years ago.

To date, based on conservative estimates from the Truth and Reconciliation Commission, approximately 4,100 to 6,000 children died amid abuse and neglect while in the residential school system. However, the Commission’s former chair, Murray Sinclair, told the CBC that the number could be as high as 25,000.

The true figure “could be in the 15-25,000 range, and maybe even more,” he said.