Broad skis don't necessarily leave tracks. One of the investigators, I'm not sure which one, said that he thought people on skis could have swooped in on the hikers from the ice about the tent. They could have also worn snowshoes, but those aren't very fast. I grew up in the far north, and for winter orienteering they taught us tricks for disguising our tracks, including having spruce bows tied to boots/skis/snowshoes. It was just for fun, but the skills were obviously some residue of conflict between settlers and Indians over fishing and hunting rights. I think the main thing is that the attackers came back later to clean up the scene.
When a crime begins, it's really fast. If you've ever been mugged, you know it happens in an instant. Unfortunately I have been a couple of times since I am an American of a certain age. They swat or swipe things out of your hands or grab them. For instance, they want a wallet but don't get a watch since it's hidden in your cuff. I think the assailants made them drop items that they saw while still preserving the element or surprise; some other items they didn't see since they were hidden, and it was night and they were on the move. I don't think the attackers were perfect--we're talking about criminals, after all.
So if we are looking for motive and opportunity, one of the Mansi noted that there were five "wild" Khanty near the pass. From a North American perspective, the Mansi are the Ojibwe, and the Khanty are the Sioux. Mansi got jobs as bounty hunters for the gulags whereas the Khanty resisted starting in the 30s. They were terribly oppressed, forced into collectivization, and criminals and dissidents moved into their territory away from the European borders. Plus their territory is mined, and their religion is based on rocks or "idols" in addition to worship of the bear. Then Soviet kids start criss-crossing their land since they couldn't travel abroad. The best indicator of future behavior is past behavior, and a very similar even happened in 1933, a "collective sacrifice" involving 7 Soviet men who were killed with rope and sleds in retaliation for the Communist woman who visited a sacred island to try to convert them to Marxist-Leninism: http://asianethnology.org/downloads/ae/pdf/a1532.pdf?fbclid=IwAR0xbE6g4dcRIW_oNSI_wME59F0vUYN39kpBJnXm3PkfNYelpsm7O5DoD6Y
So I think there were probably 3-5 attackers. There are three separate crime scenes, and it's unclear how everything happened except that the den group lived the longest. I think the attackers came back three separate times since they had hoped the hikers would die from the cold: the old gulag trick where you don't leave any traces, at least once you removed the ropes. (Most Khanty men and boys had been in the gulag at some point if they had been alive in the 30s). Maybe the last four were put in the den and a sled was run over the top of them after they were covered in snow? That is, after their bodies were laid in the stream face-down to disguise the ritual disfiguration. Those injuries are the hardest to account for as being results of conflict with other humans. And another question is whether the conflict with the Khanty was ongoing as late as 1959, but my impression is that there was a low-level ongoing war between the Soviets and the Ostyuks. There are still problems with the Manpupner rocks and the Komi people, after all: access is going to be shut off because tourists are climbing these "idols" and taking samples of them in spite of the two guards from that tribe who guard the site.