Kim "tells me he didn't know about it, and I will take him at his word," Trump said in Vietnam.
The president's comments about the Otto Warmbier case called to mind other times when he chose to believe autocrats over his own intelligence agencies, including siding with the Saudi royal family regarding the death of journalist Jamal Khashoggi and supporting Russia's Vladimir Putin's denials that he interfered with the 2016 election.
He drew a rebuke from House Speaker Nancy Pelosi, D-Calif. "There is something wrong with Putin, Kim Jong Un — in my view, thugs — that the president chooses to believe," Pelosi said.
A lawyer for the Warmbier family declined to comment.
But some prominent Republicans spoke out to condemn North Korea and express support for the Warmbier family.
"We must remember Otto, and we should never let North Korea off the hook for what they did to him," Ohio's Republican senator, Rob Portman, said in a statement.
Portman has been in contact with Warmbier's family since the suburban Cincinnati youth was imprisoned in early 2016 for allegedly stealing a propaganda poster. Warmbier died in June 2017 after being returned home in a vegetative state. His parents say he was tortured.
Trump's former U.N. ambassador Nikki Haley said on Twitter that "Americans know the cruelty that was placed on Otto Warmbier by the North Korean regime. Our hearts are with the Warmbier family for their strength and courage. We will never forget Otto."
Warmbier, a University of Virginia student had been visiting North Korea with a tour group when he was detained. A court there sentenced him to 15 years of hard labor for the alleged offense.
Last year, a U.S. judge ordered North Korea to pay more than $500 million in a wrongful death suit filed by Warmbier's parents.
U.S. District Judge Beryl Howell in Washington harshly condemned North Korea for "barbaric mistreatment" of Warmbier, awarding punitive damages and payments covering medical expenses, economic loss and pain and suffering to parents Fred and Cindy Warmbier.
Trump has claimed credit for freeing American prisoners abroad and had used Warmbier's death as a rallying cry against the North Korea's human rights abuses before softening his rhetoric ahead of talks with Kim.