Amatur aviation historian Andrey Shepelev considers that the group could die due to a photoflash bomb dropped by a US spy plane. A declassified US document confirms that in the first half of 1959 there was such a secret mission near Nizhnyaya Salda. According to Shepelev, the US plane could drop a photoflash bomb, which, due to the mountainous area, exploded closer to the ground then expected. The explosion could frighten the tourists, so they left the tent and froze to death. Some of the tourists could be injured directly by the explosion.