Non-crew members were present in the cockpit of a plane which crashed on approach to Smolensk Airport earlier this year killing the Polish president.

Lech Kaczynski and dozens of senior Polish political, military and cultural leaders were killed on April 10th, when their Tupolev Tu-154M crashed in poor weather over western Russia.

The group were en route from Warsaw to attend an event marking the 70th anniversary of the Katyn massacre - the site of the Katyn massacre being approximately 19 kilometres west of Smolensk.

This link to Katyn – in which 20,000 Polish leaders were executed by the USSR during the Second World War – prompted speculation of foul play during the crash.

However, the investigation into the crash has since ruled out the possibility of any terrorist attack, explosion, or fire on board the aircraft.

Attention is now focusing on the strangers in the cockpit during the approach to Smolensk, with Tatyana Anodinal, chief of the Interstate Aviation Committee, saying: “Some of the persons present in the cockpit were not crew members.

“The voice of one of them has been identified.

“The voice of another is still to be established by the Polish side.”

Ms Anodinal explained the voices were difficult to identify because the door to the cockpit had been opened.

In the immediate aftermath of the crash reports suggested the door to the cockpit had been opened as passengers applied pressure to the pilots to land in poor weather.

This has been denied by Poland.

Technical failure aboard the aircraft has also been ruled out by investigators, while systems at Smolensk Airport were also working efficiently.

In an interview with Russian newspaper Itar-Tass Ms Anodinal said investigators remained confident they would identify the cause of the crash, with conclusions made available to the public.