Many of the cell phones aboard the doomed Tupolev, which crashed near Smolensk on April 10 killing President Kaczyński and the other 95 people on board, were switched on at the time of the disaster and could have contributed to the crash.

A month after the crash, no concrete reason has yet been given for the tragedy, although many have been posited. Among the theories are that the Russian air traffic controllers at the Smolensk north military airport did not warn the Tupolev crew that a heavy fog had enveloped the airport. According to some sources visibility on the fateful morning was around 400 meters.

Another possible reason put forward by investigators is that the airport in western Russia was not equipped to deal with such an aircraft as the three-engine Tupolev. Journalists at the crash site saw airport maintenance crews changing lightbulbs in the landing gear on the runway's approach just hours after the crash.

According to Poland's chief prosecutor, Andrzej Seremet, the latest investigation surrounds the cell phones which were kept on board the Russian-made plane. Around a hundred cell phones were active during the last leg of the flight, Mr Seremet told daily Rzeczpospolita.

“[Passengers] called from them and sent SMSs. It may be useful in assessing if the phone use had any effect on the functioning of the instruments on the plane. This is another hypothesis which needs to be verified. It is not that the prosecution has [worked on] only a few threads of the inquiry. And those relating to the technical side will take time. Therefore, I appeal for patience and restraint in assessing the progress of the investigation,” he explained.

Mr Seremet also told radio RMF FM that his team will be questioning Jarosław Kaczyński on his last phone conversation with Lech Kaczyński. According to some sources, the president had called his brother mid flight from a satellite phone on board the plane.

The Law and Justice (PiS) party headed by Jarosław Kaczyński has put pressure on the Polish government to take over the investigation into the crash which is currently being headed by Russia. Black boxes, which contain crucial data related to the investigation, have not yet been handed over to Polish investigators.