"It's a total disgrace what happened to Otto," Mr Trump said, during an event in the Oval Office.
"It should never, ever, be allowed to happen. And frankly if he were brought home sooner I think the result would have been a lot different."
The 22-year-old Warmbier, who was released in a coma last week after nearly 18 months in detention in North Korea, died on Monday.
Mr Trump paid tribute to Warmbier's family, with whom he has spoken personally, saying "it's incredible what they have gone through."