An American student who disappeared in below-freezing conditions in Siberia more than a week ago was found dead, Russian authorities said Monday.

Investigators said the body of 25-year-old Colin Madsen was found by rescuers about a mile from the village where he vanished in the Buryatia region, the Siberian Times reported.

The cause of death is under investigation, according to a local branch of Russia’s Investigative Committee, considered the equivalent of the FBI.

Authorities said there were no obvious signs of injury to Madsen's body or any indication the young Missouri man had been robbed.

Local television reports, citing comments from police, suggested his death may have been related to drugs.

Russian authorities had launched a murder investigation in the search for Madsen, who witnesses said disappeared in below-freezing conditions after venturing out before dawn from a guest house in a mountainous region of Siberia on March 27, according to the Siberian Times.

Madsen, of Jefferson City, Mo., arrived with another American student on March 26 as part of a group from Irkutsk, where he was a university student.

According to regional media outlets, Madsen vanished from the resort village of Arshan. The tiny town is known for its mineral springs and mountainous vistas.

The Investigative Committee said in a statement last week that Madsen and his group planned to hike the mountains Sunday, but Madsen “under unclear circumstance” vanished “without a trace” as others in the guest house slept.

Madsen left all of his belongings, including a cellphone, inside the house.

Annie Madsen of Markle, Ind., said last week that her nephew, who she said is fluent in Russian and has taught English in Russia, apparently left the house without a coat to take a walk.

"He has a lot of friends concerned about him," Annie Madsen told The Associated Press about the nephew she called "a responsible young man."

"I can't see him just getting up in the middle of the night and going for a walk in freezing conditions without a coat," she said. "I don't know what was going on."

Madsen had been enrolled as a university student in Russia since the fall. The village from which he disappeared is located about 130 miles from Irkutsk.