The website of Young Pioneer Tours anticipates a frequently asked question about North Korea: “How safe is it?”

“Extremely safe!” the company replies, in an answer that remained on its site without qualification even after the return this week of one of its customers, Otto F. Warmbier, in a coma with what doctors described Thursday as “extensive loss of brain tissue in all regions of his brain.”

Mr. Warmbier, 22, a student at the University of Virginia, traveled to Pyongyang on a trip organized by Young Pioneer Tours in December 2015 and was imprisoned over alleged efforts to remove a propaganda sign from his hotel. For more than a year, North Korea declined diplomats’ requests to visit him. Then on Tuesday, it abruptly released him on “humanitarian grounds.”

Many questions remain about Mr. Warmbier’s precipitous decline in health, including whether he had been repeatedly beaten, as one senior American official suggested, citing recent intelligence reports, or slipped into a coma after contracting botulism and taking a sleeping pill, as North Korean diplomats asserted. It is also unclear why North Korea kept Mr. Warmbier’s condition a secret for so long and chose to release him now.