The tips of the birch trees barely pierced the fog. The aerial visibility on the approach to Smolensk in western Russia was just 200 metres. On its final approach, the Tupolev’s warning system repeatedly sounded: “Pull up, pull up.” But the crew of the aircraft appeared to react too late. At 10.41am on 10 April 2010, it crashed a few hundred metres short of the runway, killing all 96 people aboard.

The plane was carrying the Polish president, Lech Kaczyński, his wife, the country’s central bank chief, several MPs and its most senior military figures.

Poland fell into deep mourning, unmatched since the darkest days of the second world war. In 2011, a government inquiry blamed bad weather and pilot error. But Kaczyński’s 66-year-old twin brother, Jarosław, has never let go of his conviction that the tragedy was the result of Kremlin sabotage. Last Thursday, it came as no surprise that the Law and Justice party he leads – back in power for the first time since the crash – has launched a new inquiry.

Speaking at a ceremony to announce the new investigation, the Polish defence minister, Antoni Macierewicz, hinted at an explosion as a possible cause, saying that the plane had disintegrated above ground before crashing. “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, as he stood with relatives of the dead in front of a large screen with the words: “They are waiting for the truth, we owe them that.”

Vladimir Putin at Lech Kaczyński’s funeral. Photograph: Alexey Nikolsky/AFP/Getty Images

But the re-examination is risky. Poland is on the far-eastern flank of the EU and Nato. The stakes are higher than they were at the time of the crash, nearly six years ago. Poland has been one of the most outspoken critics of Russian policy towards the pro-Russian separatist rebellion in eastern Ukraine. At the same time, Law and Justice is hostile to Brussels, where the European Council president is Donald Tusk – prime minister of Poland from 2007 to 2014. His government is accused by Jarosław Kaczyński of having exposed Lech to danger through poor planning of the trip and by failing, after the crash, to ensure the Russians did not tamper with forensic evidence. By extension, the shadow of the Smolensk air disaster even looms over David Cameron as, in tandem with Tusk, his plan to avoid a Brexit involves assuaging the worries of potential Polish benefit claimants in Britain.

But the Law and Justice government will not allow political pragmatism to get in the way. The Polish government accuses Russia of blocking its attempts to carry out a full investigation, by failing to give it access to two air traffic controllers’ testimonies, and to hand over the black box flight recorders and wreckage. Last month, the foreign minister, Witold Waszczykowski, said in an interview with weekly pro-government magazine wSieci that the Polish government had renewed its request to Moscow for the wreckage to be returned: “In the case of a negative answer, we will build international pressure,” he said.

“I think that if Russia has not shared credible information for years, if Russia manipulates the investigations, does not return the wreck, they put suspicion on themselves. When someone acts like this it means they have something to hide,” Waszczykowski added.

The new commission of inquiry is due to start work in March. It has 21 members, many of them engineers or technical experts, and four advisers from abroad. The news of its launch worries many Poles, including opposition politician Ryszard Petru. He says the new inquiry is “all about revenge and to send a few people to prison”.

While in opposition, Law and Justice party members produced evidence of foul play, often in online videos whose accuracy is impossible to verify. The films include people presented as experts using props such as crushed tins and sausages to explain that the aircraft exploded mid-air before crashing. Many of the films have been dismissed as using old footage, taken off the internet. One newspaper even reported an expert claiming that a fog-making machine had been used to create poor conditions of visibility at Smolensk.

Władysław Kosiniak-Kamysz, chairman of the Farmers’ party, told the Polish press agency: “The commission will create more versions, maybe more myths, and scars will be ripped open for the families of the victims. It will lead to a deepening of the divisions among Poles.”

After the crash, many widows and relatives joined Law and Justice, with some building political careers and even entering parliament. Others reacted negatively to Law and Justice’s mission to keep probing the cause of the crash. On Thursday, Małgorzata Sekula-Szmajdzińska, widow of deputy speaker Jerzy Szmajdziński, told television channel TVN24: “This [new investigation] is just politics. I do not want to have anything to do with it.’’

Smolensk is significant in Polish history because it is close to the place where Stalin’s secret police shot some of the 22,000 Polish officers and intellectuals they executed in 1940. The massacre is an enduring symbol of Poland’s suffering at Soviet hands, and Lech Kaczyński had been flying in to commemorate it. On the 10th day of every month, friends and family of the Smolensk victims light candles in their memory on the paved forecourt outside the president’s residence in Warsaw.

Reminders of Smolensk are constant in Poland. Many relatives of the victims have accepted the findings of the initial inquiry. But others, especially people close to the Kaczyński clan and Law and Justice, continue to seek culprits. Next month a court case initiated by victims’ relatives resumes against Tusk’s former chief of staff and two of his aides.

Jarosław Kaczyński (centre) … back in power. Photograph: Sławomir Kamiński/Agencja Gazeta/Reuters

Others still, such as Macierewicz, deputy leader of Law and Justice, have expanded their political careers around surviving twin Jarosław Kaczyński’s tireless quest to disprove claims that his brother put undue pressure on the pilot, Arkadiusz Protasiuk, to land, despite atrocious weather conditions.

Jacek Kucharczyk, president of the Institute of Public Affairs in Warsaw, believes the reason for the crash is far more prosaic. He says: “Lech Kaczyński’s ratings were down. He was flying to Smolensk to open his election campaign. He was determined to be on time. Nobody wanted to take responsibility for diverting the plane. The media had made a joke of Kaczyński’s planes always breaking down.”

The Kaczyński twins had been features of Polish life long before Lech’s presidency, or the Smolensk crash. As 13 year-olds, they played the leads, Jacek and Placek, in The Two Who Stole the Moon, a 1962 children’s film. As adults, they remained impossible to tell apart, except for the cat hairs that could sometimes be spotted on Jarosław’s dark clothes. Of the two, Lech was the more likable, with a sense of humour and fun, and a successful marriage. Jarosław cannot drive or use a computer, seems to live as a recluse and is an eternal bachelor. But he was always politically more astute than his brother. They needed one another.

“In the past, it was very easy to ridicule the Kaczyńskis as the Two Who Stole the Moon,” says Kucharczyk. “Now Jarosław is dangerous. He seems to be using his brother’s memory, and he may be vengeful. He is dangerous because he is not elected but is ever-present in Polish political life, and we do not know what is going on in his mind.”

Macierewicz has cast himself as the main champion of the sabotage theory. In March this year, he seemed to hint for the first time at a clear Russian motive for downing the plane. “Putin is fully responsible for this tragedy,” he told the European parliament. “It was the first salvo in a war which today is going on in the east of Europe, and which is ever more dramatically nearing the EU and Nato borders.”

Lech and Jarosław Kaczyński in the The Two Who Stole the Moon in 1962. Photograph: East News

Since coming to power in the 25 October parliamentary election, Law and Justice has expanded the Kaczyński cult. In December, the Polish parliament held a commemorative regional conference in Lech’s honour. MPs commemorated the 10th anniversary of his oath of office and President Andrzej Duda named a conference hall after him. Swiftly after the election, the Tusk-era Miller investigation into the Smolensk crash was removed from the Polish government’s website.

A number of recent legal changes, rushed through since Law and Justice came to power, may also serve Kaczyński’s plan to keep memories alive of the Smolensk tragedy. The European Commission is investigating the legality of the government’s apparent attempts to hamper the work of the constitutional tribunal – the highest court in the land – and a move to sack public broadcasting chiefs.

Other legal changes rushed through in the past three months include new internet snooping powers for the police and, last week, a move to shift the attorney general’s office into the justice ministry. There has been no suggestion that the law changes have deliberately been carried out ahead of the launch of the new Smolensk investigation. But each could in its way prove useful if, as Petru claims, the Law and Justice government has already written the conclusion of the new inquiry.

Even if the government does not have a preconceived outcome in mind, analysts say Law and Justice is keeping alive the memory of the Smolensk disaster as a power ploy, feeding into a romantic nationalistic notion that those who died in the crash are “the fallen”, thus assimilating them into a tragic nation’s history; its latest, perfect heroes.

Kucharczyk says: “The focus on Smolensk fits in with the Polish proclivity for celebrating mass deaths and disasters. We are very good at that. Law and Justice is the party of national mourning. The crash somehow struck a chord with the national psyche, if you believe in such things.”

Add the birch trees piercing the thick fog on the plain, the setting at Smolensk and the Russian bogeyman. These are the ingredients of a perfect cold war drama for a nation with a lasting need for martyrs.