The remains of the former Polish president Lech Kaczyński and his wife Maria are to be removed from the crypt at Wawel Castle in Kraków on Monday evening and re-examined by state prosecutors.

The move is the latest step in the ruling Law and Justice party’s efforts to demonstrate that the Smolensk air disaster in April 2010, which killed the pair and 94 others, was engineered by Russia and covered up by domestic political opponents.

There are expected to be exhumations of 10 Smolensk victims this year, with a total of 83 victims to be exhumed and re-examined by the end of 2017. According to polling by Ipsos, only 10% of Poles support the move, and the planned exhumations have sparked protests among some of the victims’ relatives.

In a letter to political and clerical authorities, more than 200 relatives of 17 people who died wrote: “Six years after those terrible days we stand alone and helpless in the face of a ruthless and cruel act: our loved ones are to be taken out of their graves … We, the families, have for months unsuccessfully expressed our objection to the announcement of this incomprehensible and unjustified venture.”

In a speech during a ceremony on 10 November, the day before Poland’s independence day, the Law and Justice leader Jarosław Kaczyński, Lech’s twin brother, declared the country would not be free until the truth about Smolensk had been established.

“There will not be a free Poland, a truly free Poland, without the truth, without a proper honouring of those who died, without a closure of this case which has cast such a long shadow on our national and social life,” he said.

A series of investigations since 2010 have concluded that the state-owned Tupolev 154, which was flying a presidential delegation to a ceremony in Katyn forest in western Russia to mark the 70th anniversary of the massacre of more than 20,000 Polish officers at the hands of the Soviet NKVD, crashed as a result of hazardous fog, pilot error, and poor communication with Russian officials on the ground.

But senior Law and Justice politicians have long rejected the findings, suggesting instead that Kaczyński was murdered, possibly as revenge for his outspoken opposition to Russia’s actions during its war with Georgia in 2008.

After sweeping to power in elections in 2015, Law and Justice removed from the government’s website the report published in 2011 by a state-appointed body of aviation experts, and disbanded the military prosecutor’s office that had been responsible for investigating the crash.

While Law and Justice was still in opposition, Antoni Macierewicz, now defence minister, formed a parliamentary commission to investigate the crash. That commission suggested in 2014 that there had been a mystery explosion on the aircraft. Commission members did not have access to the crash site, however, relying on photographs and information obtained from the internet, and experiments involving props ranging from tin cans to sausages.

In one high-profile gaffe, the expertise of one member of Macierewicz’s commission was revealed to have been based upon experience of constructing model aircraft, sitting in a fighter jet’s cockpit during an air show, and observing plane wings while looking out of a passenger window.

Macierewicz, the most vocal proponent of the notion that the disaster occurred as the result of an attack, has described the crash as “aimed at depriving Poland of its leadership, which was leading our nation to independence”, and the official Polish investigation as the greatest cover-up “in the history of the world”.

Announcing a new state investigation earlier this year, Macierewicz asserted that the plane “disintegrated” metres above the ground before it crashed. “There is no doubt that these circumstances are not only a sufficient reason, but one that makes it compulsory to re-examine this tragedy,” he said.

Government officials cite this and a number of alleged irregularities in previous investigations as justification for the exhumations, to the outrage of some relatives.

Senior Law and Justice officials have expressed their sympathy, but argue the decision lies with prosecutors, and that the exhumations may be a distressing necessity. Some other relatives have expressed their support for the exhumations.

Government critics, however, argue that Law and Justice may be motivated more by a desire for revenge than for the truth about the crash.

Jarosław Kaczyński has long suggested that the centrist government of longtime rival Donald Tusk, Poland’s prime minister when the Smolensk disaster occurred and now president of the European council, bears responsibility for the alleged cover-up, telling him in the Polish parliament in 2012: “In a political sense, you bear 100% responsibility for the catastrophe.”

Defending the exhumations in a recent interview with the Onet news site, Kaczyński said the “investigation by the previous government was a scandal, for which many people should face the legal consequences”.