Trudeau made the comment Tuesday after facing angry chants by some attendees of a memorial ceremony at the former residential school in Kamloops, B.C., the day before.
"There were a number of people who are still very, very hurt by this and who are angry, and, frankly, they have a right to be angry," Trudeau said at an event in Vancouver, where he was visiting a family to discuss federal housing policy.
The ceremony in Kamloops on Monday marked one year since the Tk’emlups te Secwepemc announced that ground-penetrating radar had identified 215 suspected graves in an apple orchard by the former residential school.
The announcement sparked a reckoning over Canada's treatment of Indigenous Peoples and additional searches on former residential school grounds across the country.
Trudeau said the news affected Indigenous people who have long known that many kids who went to the schools never came home, as well as Canadians who learned with shock that residential schools had graveyards.
"These are things that Canada needs to grapple with and, of course, there's a need for healing, there's a need for partnership, but there's also going to be a lot of trauma and anger," Trudeau said.
He said he was "incredibly touched" by elders who welcomed him and told him it was important for the federal government to be at the ceremony and he also understands there are others who are still very hurt.
Hundreds of people attended the daylong memorial in Kamloops and Trudeau was followed by a large group who chanted and pounded drums as he stopped in the stands, talking face-to-face with people.
'They have a right to be angry': @JustinTrudeau says residential school legacy ongoing. #CDNPoli #ResidentialSchools #IndigenousChildren
While he exchanged hugs with some, others were less receptive, chanting, "Canada is all Indian land," and "We don't need your Constitution.'"
"Canada was responsible for horrific things happening to Indigenous people, and those injustices continue not just in the past, but in the present today," Trudeau said Tuesday.
Socio-economic inequality and mental health challenges are among the legacies of residential schools that require ongoing action, he added.
"I was grateful to be there, grateful to hear people's perspectives, and grateful to be able to continue to insist and demonstrate that the federal government will be there as a partner on reconciliation for the long term."
This report by The Canadian Press was first published May 24, 2022.