US Student Missing in Siberia Found Dead Colin Madsen, 25, has been found dead by police a week after he vanished.

MOSCOW  -- A U.S. student missing for over a week in eastern Siberia has been found dead, Russian investigators said today.

Colin Madsen’s body was found by rescuers about a mile from the village where the Missouri man had disappeared in the Buryatia region, investigators said in a statement released by the local branch of Russia’s Investigative Committee, the equivalent of the FBI.

Russian police had earlier opened a possible murder inquiry into Madsen's vanishing in the foothills of the Sayan mountains, roughly 3,000 miles from Moscow, where a search for the student has been gradually intensifying since last Monday.

But today’s statement said that there were no signs of outward injury on Madsen’s body or any indication he had been robbed. Investigators said a cause of death has not yet been established but the statement suggested that it may be related to drugs.

Police are now testing Madsen’s body for traces of narcotics and the statement noted that the group with which Madsen had been travelling had taken drugs in the day before his disappearance.

Police today said the murder inquiry remained open while the full circumstances around Madsen’s death were established.

Madsen, 25, a native of Jefferson City, Missouri, who was studying at a university in the nearby city of Irkutsk, vanished a week ago early on a Sunday morning in the Sayan mountains, where he was on a hiking trip with friends. The manner of his disappearance has puzzled police and his friends: Madsen left the guest house where the group was staying in the village of Arshan, without warning at around 5 a.m. and wearing only a T-shirt and trousers despite freezing temperatures outside. He had not been seen since.

Dozens of officers, as well as a number of Madsen's local friends, had been searching forests around the village for him since then.

Madsen had been traveling with three friends, two local Russians and another American student, on exchange at the same university. The friends have told police that Madsen had intended to join them on an early morning hike but when they woke up they found him missing and all of his equipment still laid out.

A number of Madsen’s friends have told ABC News that it was uncharacteristic of him to leave without warning in the middle of the night or without appropriate clothing. The friends traveling with him have told police Madsen had been behaving normally before he disappeared and that he was excited for the day’s hike. Police have said the group had not quarreled in the day before Madsen left.

Madsen had been studying in at Irkutsk State Linguistics University since 2013 and had repeatedly visited the area around Arshan, friends said. He knew the area well and spoke fluent Russian.

Madsen’s body has been transferred to the city of Ulan-Ude for testing. His mother is already in eastern Siberia, where she had arrived to participate in the search.