Russian aviation officials said on Wednesday that at least two non-crew members were in the cockpit of a Polish plane before the crash that killed all 96 on board, including President Lech Kaczynski and his wife.
Edmund Klich, head of a Polish committee that analyses airplane crashes and is also participating in the IAC examination, said recordings showed the voices of non-crew members were heard in the background 16-20 minutes before the crash.
Tatiana Anodina, head of Russia's Interstate Aviation Committee (IAC), said the voice of one of the passengers had been identified, while the other, or potentially others, were still being analyzed.
"This is important for the investigation," Ms. Anodina told journalists at a briefing. She declined to identify the voice, citing moral reservations and international rules.
"I do not believe that this will have a decisive influence on the cause of the catastrophe," Mr. Klich said. "But this is my personal opinion."
He added that the presence of non-crew in the cockpit did not break any rules since government and military planes are governed by different standards. Passengers are not allowed in the cockpits of civilian aircraft.
Russia's IAC added that its analysis had ruled out an attack, an on-board fire or mechanical failure as reasons for the Polish Tu-154 military plane to crash, leaving the potential reasons of bad weather and human error still open.
"The engines worked up to the moment of hitting the ground," Ms. Anodina said.
The IAC's preliminary report did not provide its conclusion on the cause of the plane's crash, which took place in thick fog near Russia's Smolensk airport on April 10.
But the preliminary findings confirmed earlier reports that weather conditions limited visibility to dangerous levels and that the Polish plane should not have landed in the dense fog.
Based on information analyzed by the IAC, the visibility was limited to around 200 meters 11 minutes before the crash.
Alexei Morozov, an IAC official, said that the crew, which had been put together only a few days before the flight and lacked training on handling special flight situations.
However, Mr. Morozov said that the preliminary findings were not to "serve to establish a partial fault of whomever or their responsibilities, and should not be taken as such."