© RIA Novosti. Oleg MineevKaczynski Plane Debris
A Polish prosecutor and four experts are conducting an additional examination of seat fragments in the debris from a jet that crashed in Russia in 2010, killing Poland's then-president, Lech Kaczynski, the Polish Main Military Prosecutor's Office reported.

An Office spokesman said the Polish delegation's visit to Russia had been coordinated with the Russian side beforehand. The experts will work in the western Russian city of Smolensk until the end of next week.

The Russian-made Tu-154 jet, carrying Kaczynski, his wife and a host of top officials, crashed in heavy fog as it attempted to land at an airfield near Smolensk on April 10, 2010. The delegation was flying to Smolensk to mark the 70th anniversary of the 1940 Katyn massacre of thousands of Polish officers by Soviet secret police. All 96 people aboard the plane died.

Last fall, the Polish newspaper Rzeczpospolita claimed that traces of explosives were discovered on the plane's debris. Military prosecutors denied the claims, saying the final results of chemical tests would be made public in six months. The newspaper's editor-in-chief resigned following the publication.

(Click here to see infographic "The plane crash that killed the Polish president")
© RIA Novosti. Oleg Mineev
Ireneusz Szelag, head of Warsaw's district military prosecutor's office, in June told journalists that tests had not revealed any traces of explosive devices or products of their decomposition on the plane debris.

However, Szelag said, the conducted research is "insufficient to make a conclusion of a possibility of explosive changes near the examined objects."

Russian and Polish investigators carried out a joint investigation from February to March this year in response to speculation that the late Polish president could have been the victim of a conspiracy to blow up his plane with a bomb.
© RIA Novosti. Oleg Mineev
Russian Investigative Committee spokesman Vladimir Markin said at the time that investigators had examined "trees and aircraft fragments and took more than 300 samples for comparative tests carried out in Russia and Poland," concluding that "the examined objects carried no traces of an explosion."

In its probe into the air crash, the Moscow-based Interstate Aviation Committee said the Polish flight crew was responsible for the accident. Poland, which carried out a separate investigation, partially blamed Russian air traffic controllers.

(Click here to watch MAK video reconstruction of Polish president's Tu-154 crash)