The theories were countless, including a snatching by a yeti (or by the Mansi tribe which lived in the area.) Visitors from outer space were proposed, but none of the suggestions made sense once it was determined that the slash in the side of the tent was made from the inside. Lev Ivanov, who headed the investigation, pronounced that the situation was due to "an unknown compelling force."
Enter Donnie Eichar who was fascinated by the incident and determined to shed light on it. To do this successfully, to follow the footsteps of the hikers and to write a compelling book would, I imagine, require that the investigator be a good writer, reasonably versed in Russian and accustomed to crossing large expanses of snow and ice. Donnie Eichar is a film maker, but the two other people who appear on the jacket must have been used as co-writers. His Russian is non-existent, and that was a distinct problem (though bits of Russian songs and poems are interspersed with the text to give it a Russian feel.) As for experience, he says, "I had seen snow less than a dozen times in my life."
Nevertheless, I give him credit for his resolute determination to solve the whole question of what happened to the Dyatlov party. He does a believable job. You will have to read the book. Spoiler alert—Karman vortex.