Poland closes 10-year 'diplomatic treason' probe into Smolensk crash cooperation with Russia

The final decision

Poland's National Prosecutor's Office has closed the last five threads of an investigation into alleged diplomatic treason connected to the 2010 Smolensk air disaster, ending the case in its entirety. The probe, launched on 31 August 2016, examined whether Polish officials acted against the country's interests by choosing Annex 13 of the Chicago Convention as the legal basis for cooperation with Russia in the crash investigation. Prosecutor spokesman Przemysław Nowak told a Wednesday press conference that the decade-long inquiry found no evidence of criminal conduct.

“The investigation conducted over 10 years showed that the behaviour of the Polish authorities in April and May 2010 did not exhaust any elements of the crime of diplomatic treason.”

Nowak added that the authorities did not act to the detriment of the Republic of Poland and had no such intention. In March 2026, two partial discontinuance decisions were issued. The latest ruling, made on 31 July and announced on 5 August, covers the remaining five threads and formally concludes the entire proceeding.

The legal choice under scrutiny

The core of the case was the decision by then-Prime Minister Donald Tusk and other public officials to accept Annex 13 of the Chicago Convention on International Civil Aviation as the framework for the crash investigation. Critics argued that the military status of the Tu-154M flight meant the convention, designed for civil aviation, was inappropriate and gave Russia disproportionate influence over the inquiry. Prosecutors examined four possible cooperation models and concluded that the chosen path was the most advantageous for Poland at the time.

“None of the alternative solutions considered offered a real possibility of more effectively safeguarding the interests of the Republic of Poland.”

The investigation involved 488 witness interviews, extensive documentation including copies of four legal opinions, and requests for international legal assistance sent to several countries. Notifications that triggered the probe were filed by the Solidarni 2010 association and individuals including Antoni Macierewicz, who alleged that officials deliberately selected a legal basis harmful to Poland.

Sikorski's sharp reaction

Foreign Minister Radosław Sikorski, one of the officials targeted by the accusations, responded forcefully on social media platform X. He referenced his earlier civil case against PiS leader Jarosław Kaczyński, who was ordered to apologise for accusing Sikorski of diplomatic treason. Sikorski proposed that Kaczyński instead pay 50,000 złoty to Ukraine's armed forces, which Kaczyński did in January 2023.

“Now confirmation from the National Prosecutor's Office: there was no diplomatic treason, nor any intention to commit it.”

Sikorski went further, stating that none of the "Smolensk liars" would apologise. He accused them of deceiving millions, dividing families, and stirring hatred within the nation, adding that they would "burn in hell for it" but had gained power, money, and satisfaction in return.

The main investigation continues

While the diplomatic treason case is now closed, the primary investigation into the crash itself remains active. Nowak said that probe, opened in 2010, is "undoubtedly heading towards its conclusion." A supplementary opinion from an international team of experts has recently been translated and shared with the parties, victims, and their legal representatives. Nowak declined to disclose the findings but said a public update is a matter of weeks away. Victims will have the opportunity to challenge the opinion and submit additional evidence requests.

The 2010 disaster

On 10 April 2010, a Tupolev Tu-154M carrying 96 people crashed near Smolensk, Russia. All aboard were killed, including President Lech Kaczyński, his wife Maria, and a delegation of Polish officials and families of Katyń massacre victims travelling to commemorate the 1940 Soviet atrocity.