"I can see only two other options.
1)Staged by outsiders , which leaves a lot of work and logistics to cover up. That's witnesses at airports, fuel, families of stagers , footprints, roaming random Mansi hunters, fighting weather conditions, covering up tracks, leaving nothing behind to incriminate the stagers , the camera's etc ....."
from what I know of the cold war, limited at best, that was pretty much standard operations