There were irregularities in the Russian investigation, Polish experts say AFP/East News

Polish experts have found traces of explosives on the wreckage of the presidential plane that crashed in Smolensk in April 2010, killing President Lech Kaczyński and 95 others, reported Rzeczpospolita Tuesday. The experts have been investigating the wreckage of Tu-154 for the last month, after Polish prosecutors expressed doubts regarding the Russian specialists' analysis of the pyrotechnics.

The analysis delivered by the Russians did not meet some procedural requirements, the newspaper reports, which is why a team of Polish experts – including specialists from the Central Forensic Laboratory and the Central Bureau of Investigation – was sent to Smolensk to carry out its own detailed investigation.

Using the most technically advanced equipment, they found some significant traces of explosives both inside the aircraft and on its wings. Devices detected traces of TNT and nitroglycerine also on 30 seats.

Poland’s attorney general and Prime Minister Donald Tusk have already been informed of the discovery, and are now deciding what steps should be taken next. Experts can’t unambiguously determine why traces of TNT and nitroglycerine were found on the wreckage.

One hypothesis, however, is that the traces could be remnants of explosives from World War II. During the war, heavy fighting took place in the Smolensk region.

The plane was carrying the president, his wife, and other politicians, military personnel and dignitaries who were traveling to Smolensk to attend ceremonies marking the anniversary of the 1940 Katyn massacre, in which Soviet security forces executed tens of thousands of Polish officers and members of the intelligentsia.

Poland A.M.