The leader of the right of center governing Law and Justice (PiS) Jaroslaw Kaczynski's twin brother, then president Lech Kaczynski, was among 96 people - most of them senior Polish state officials - who died in the crash in Smolensk, western Russia, on April 10, 2010.

The delegation was heading to a ceremony for thousands of Polish army officers killed by Soviet secret police in 1940 in Russia's Katyn forest - a massacre Russia denied until 1990.

Some 83 of the victims' remains will be exhumed in an investigation that is reportedly likely to last at least two months and cost about 10 million zlotys (2.3 million euros, $ 2.49 million).

Prosecutors have been briefed to check that the remains have been correctly identified and also to test for traces of explosives. The first bodies to be exhumed will be Kaczynski and his wife Maria, with the chief of the general staff, the heads of all three armed forces, the director of the intelligence service and the president of the national bank to follow.

Kaczynski and his wife Maria are buried in the crypt of the Wawel royal castle in Krakow where the kings of Poland are also interred.

Rest in peace? 

Only 10 percent of Poles approve of the decision to exhume the bodies, according to a survey published last month by the IPSOS pollsters.

"The investigation challenges rational thinking - what we can be expected to find after five years and after what happened with the bodies during the crash itself," says Warsaw-based sociologist Joanna Srednicka. Most Poles are simply very tired of all this," she told DW.

Last month, more than 200 relatives of 17 of the 96 victims wrote an open letter to President Andrzej Duda, saying they felt "abandoned and distraught in the face of a cruel and heartless act" of exhuming the remains. The relatives were backed by Poland's ombudsman, who argued they have the right to appeal.

PiS wants to keep digging 

PiS believes a fire may have started onboard before the crash. The PiS-led government, which came to power in October 2015 after eight years in opposition, launched its own investigation in early 2016. They point out that, according to prosecutors findings in June, six of the previously exhumed nine bodies had been wrongly identified.

PiS insists that it was an assassination inspired by the Kremlin as punishment for Lech Kaczynski's support for Georgia during its armed conflict with Russia. Moscow vehemently denies the allegations. 

To date, there have been two investigations - one Polish and the other Russian - into the causes of the crash, which took place as pilots attempted to land a Soviet-made TU-154 in heavy fog at a small airport near Smolensk. Defense Minister Macierewicz said in June that the plane had "disintegrated" meters above the ground. Both Polish and Russian investigations found no evidence to support the claim. Kremlin spokesman Dmitry Peskov said in March that Polish suspicions were "groundless, biased and having no connection with the real circumstances of this aircraft accident."

Conspiracy theories abound. Many believe there was collusion between previous ruling party Civic Platform (PO) and the Kremlin. Moscow has been asked to hand over the wreckage and black boxes to the Polish authorities. The new Polish commission re-investigating the crash in September has accused its predecessors of doctoring evidence and manipulating facts.

Facts and fiction

Appointed by Macierewicz, the new investigation team announced its preliminary findings in September, saying that the 2011 Polish report was the result of "falsifying, manipulating, avoiding, and hiding” the truth.

"Some of the elements were tampered with," commission head Wacław Berczynski argued. According to his colleague Kazimierz Nowaczyk, three seconds had been cut from one of the black-box recordings, while five seconds were deleted from the other. They showed secret footage of the commission's head - then interior minister Jerzy Miller, - seeming to suggest that their report should be in line with the Russian one so as to avoid any questions about inconsistencies and "conspiracy theories."

Maciej Lasek, head of the committee for investigation of national aviation accidents, told the Russian news agency Tass that no-one had deleted anything from the black-box recordings.

Poland's previous liberal government, led at the time by Donald Tusk, Jaroslaw Kaczynski's main rival and currently President of the European Council, blamed bad weather and errors by the Polish pilots and Russian air traffic controllers.

The Tusk-appointed previous investigation team said in 2011 that the crash was a result of Polish pilot error and poor guidance by Russian controllers in dense fog and poor visibility. A separate report by Russian experts blamed the Polish crew and the alleged presence of a Polish air force commander in the cockpit.

Political context 

President Lech Kaczynski was vociferous in his attacks on Russia, and in particular in his support for Georgia during its 2008 war with Moscow. He reportedly ordered pilots to land in Tblisi without the requisite security guarantees to fly into a war zone on such short notice in 2008. This lead many to believe the pilots in the Smolensk disaster could have come under similar pressure to land. 

"The Smolensk catastrophe is one of the 'founding myths' of PiS and a foundation uniting its electorate," says Warsaw-based political scientist Jan Mus. Even excluding conspiracy theories - such as the one about the Russians billowing artificial fog over the airport shortly before the plane landed - there is still room for speculation, he told DW.

"Moscow very skillfully fuels them by keeping the wreck of the airplane under its control," Mus says.

2010 was also an election year for an unpopular president who had overseen Poland's often shambolic drift into dysfunctional cohabitation- as some have called it - with the executive divided between Kaczynski's presidency and Tusk's government under PiS's main PO rival.

"Macierwicz has made no light of the fact that he regards the accident as an assassination," Jan Darasz, a historian of Warsaw, told DW, adding that the Defense Minister consistently used the word 'polegli', meaning 'fallen in battle' to describe the deaths of those who did indeed die in the line of duty.

"This is a semantic usage but a clever and skilful one as it conflates an air disaster that has not yet been fully explained, with the 'glorious dead' in war," Darasz says.

"The crash triggered a sequence of ritual behavior," Dariusz Czaja, a professor of ethnography at Krakow's Jagiellonian University, told DW. "Such mourning drama and was designed to unite the politically divided national community, although it had exactly the opposite effect."