It gets weirder. The final four were better outfitted than the other five, and apparently had taken clothes off the dead as they continued their aimless trek. Zolotariov, for example, was found wearing Dubinina's coat and hat, while she in turn had wrapped around her foot a piece of the wool pants that one of the two found at the pine tree had been wearing. To add to the mystery, the clothes found on the final group were tested and found to be radioactive.
Documents related to the case were sealed after it was closed, and weren't opened until sometime in the 1990s. I've been interested in the case for awhile now and have tried to dig up new info, but my FOIA requests to the various US intelligence agencies have all turned up bupkis. The cause of the incident is still speculative, but interviews given by the lead investigator, Lev Ivanov, around the time the records were unsealed shine light on just how strange the case is.
Ivanov was the one who first noticed that the bodies and gear found were all radioactive, and said that a Geiger counter he'd brought with him went nuts all around the campsite. He also has said that Soviet officials told him at the time to clamp the case shut, despite reports that "bright flying spheres" had been reported in the area in February and March of 1959.
"I suspected at the time and am almost sure now that these bright flying spheres had a direct connection to the group's death," Ivanov told Kazakh newspaper Leninsky Put in an interview dug up by the Times.
Another group of students camped out around 30 miles from the other group reported similar sightings at that time. In written testimony, one said that he saw "a shining circular body fly over the village from the south-west to the north-east. The shining disc was practically the size of a full moon, a blue-white light surrounded by a blue halo. The halo brightly flashed like the flashes of distant lightning. When the body disappeared behind the horizon, the sky lit up in that place for a few more minutes."
The leading theory, considering the secrecy, radioactivity, and the appearance of some of the bodies, which were reported as being "deeply tanned" by a young boy attending some of their funerals, is that the group somehow came across a Soviet military testing ground. But, assuming reports are true, what caused the trauma to some members of the group is unknown.
It's possible that one of the members saw some crazy light in the sky and everyone freaked out, running for their lives, but there has never been evidence of an explosion in the area, ruling out some sort of nuclear test or something of the like. But even so, that doesn't explain the skull fractures. Some could be explained by a fall into the ravine, but remember, Slobodin had a fractured skull and was found on his return to the camp.
The fact that remains of a fire were found suggests some members of the group had control of their mental faculties, and psychosis isn't a reported effect of acute exposure to radiation, but that doesn't explain why the group appeared to have run for their lives without bring any of their gear. So was it an accident or a cover-up? Ivanov, the investigator, has since passed away, and unless more military records are discovered and unsealed - which some advocates still call for - the records on hand aren't enough to prove otherwise, and the mystery of what's now known as the Dyatlov Pass is likely to endure.