Some members of the Dyatlov group during the expedition.
CNN  — 

Russian prosecutors have launched a new investigation into the mysterious case of nine students who died in bizarre circumstances after disappearing on a skiing trip 60 years ago.

Countless articles, books and documentaries have sought to explain the fate of the group from the Ural Polytechnic Institute who set off on the trip in 1959 under the direction of Igor Dyatlov, a fifth-year student.

Igor Dyatlov

The Dyatlov Pass Incident, as it came to be known, has been compared with other unsolved mysteries, including the disappearance of Lord Lucan, the British aristocrat who vanished after his children’s nanny was found murdered, and the abandoned ship, the Marie Celeste. It has inspired many theories over the decades – but now the authorities are aiming to get to the bottom of it once and for all.

Nobody has so far managed to uncover solid proof of why the group of experienced hikers fled their tents in a remote camping spot while partially clothed and without footwear. Their bodies were discovered over the following weeks in the snow, with several having suffered serious head wounds.

The seven men and two women set off on the ski trip on January 23, 1959. Their 16-day itinerary aimed to cover 190 miles and cross the North Ural mountains: Otorten and Kholat Syakhl. The plan had been to make contact by telegram from the final point – a village called Vizhay – but this never happened.

A search operation was launched on February 20, and six days later the students’ tent, which had been sliced open, was discovered. The following day the bodies of Yuri Doroshenko and Yuri Krivonischenko were found just over a mile away. Lying by a campfire, they were both stripped to their underwear.

Rescuers found the group's tent abandoned and cut open

In the days that followed, three more of the skiers were dug up, including Dyatlov, while the remaining four were only found in May once the snow had melted.

A criminal case was opened at the end of February, but it was closed three months later having concluded that the “spontaneous power of nature” was to blame. The Soviet-era investigation remained classified until the 1970s, the AFP news agency reported.

For many, this explanation was far from satisfactory as it failed to explain why the adventurers had rushed out into the freezing cold wearing only underwear and without shoes. Nor did it address why several of the group had suffered broken bones and skulls.

Some 75 theories have been put forward, according to the prosecutor’s office – including an alien abduction. Another suggests they were killed by members of the Mansi people, for whom the mountains were spiritually symbolic. Still others claimed the scene was staged in order to cover up details of a secret weapons testing program.

However the new inquiries will only investigate three theories considered the “most likely ones.”

“All of them are somehow connected with natural phenomena,” said Alexander Kurennoi, the official representative of Russia’s Prosecutor General.

“Crime is out of the question,” he said, adding: “There is not a single proof, even an indirect one, to favor this (criminal) version. It was either an avalanche, a snow slab or a hurricane.”

“Relatives, the media and the public still ask prosecutors to determine the truth and don’t hide their suspicions that something was hidden from them,” Kurennoi said in a video posted on an official website.

Appearing at a press conference, a spokesman for the prosecutor’s office for the Sverdlovsk region revealed a 400-page volume of original case materials.

Investigation files seen during the press conference

Andrey Kuryakov told the news conference that investigators were relying on the help of “friends and family of the deceased” as well as modern technology, which was not available at the time.

Andrei Kuryakov and journalists during a press conference on the reopening of the investigation into the  Dyatlov Pass Incident.

Also at the press conference was Petr Bartolomey, a friend of Dyatlov. He said: “A year prior (to the incident), we went to the Subpolar Urals in an expedition, where the conditions were much more difficult than his last venture. I have always characterized him as a wonderfully knowledgeable person, an athlete, always well-prepared … One could always rely on him.

“I can say the same for the rest of the guys, although we did not go on as many expedition(s) as with Igor. I am glad that, years after, a high-level investigation is resumed to understand what exactly happened.”

Next month prosecutors will fly to the site, and a range of experts and rescue workers will be involved in the investigation. Experts will conduct nine different examinations, including a forensic probe, which will help to fill in “a number of blank spots,” Kurennoi added.