Wreath-laying ceremonies, church services, demonstrations: throughout the country on Monday, Poland commemorated the plane crash near Smolensk in western Russia seven years ago. The accident killed president Lech Kaczynski, along with 95 other people, including military chiefs of staff, politicians, clerics and high-ranking civil servants. They had been on their way to attend a memorial ceremony at the site of the Katyn massacre. There, as well as in a number of other places, the Soviet secret police had executed some 22,000 incarcerated Poles during World War II.

After the crash in 2010, a Polish government commission concluded - very much like its Russian counterpart - that the most likely cause of the accident was the pilots' attempt to touch down despite heavy fog.

However, the domestic dispute concerning the background and aftermath of the crash appears to be growing ever more serious. Lech's twin brother, Jaroslaw, is the head of the national-conservative governing party, PiS (Law and Justice). He has thus far held then-Polish prime minister and current Europan Council President Donald Tusk to be morally complicit in the disaster. Prior to the memorial service, Tusk had made efforts to organize Lech Kaczynski's visit separately from his own - a fact which led to unending speculation and accusations on the part of Tusk's detractors.

Charged with treason

The dispute has now become an issue for Poland's judiciary. Defense Minister Antoni Macierewicz has filed charges against Donald Tusk with regard to the Smolensk crash. He is accusing Tusk of "diplomatic treason," which can be compared to the statutory offense of "treason" in other nations. In Poland, "diplomatic treason" is punishable by up to 10 years imprisonment. Apparently, charges have been filed only for the time period after the plane crash. The Tusk government, the charges maintain, committed serious errors when it handled the crash investigation with Russia and was too lenient vis-a-vis Moscow.

Poland commemorates the plane crash near Smolensk seven years ago

According to Macierewicz, Tusk did not fulfill his duties and carelessly handled the investigation into the causes of the accident over to Russian authorities. In addition, Tusk had not done enough to enforce the return of the plane wreckage to Poland, which had been promised by then-Russian president Dmitry Medvedev. The same applied with regard to efforts to return flight data recorders. To this day, both the wreckage and flight recorders remain in Russian hands.

In March, Warsaw was able to win over an ally who may be able to help retrieve the wreckage from Russia: Argentinian Luis Moreno Ocampo, who was chief prosecutor at the International Criminal Court in The Hague until 2012. Moreno Ocampo told Poland's "Dziennik" newspaper that he wanted to make a contribution "exclusively as an expert and consultant in the context of international law," intending to submit an "independent opinion."

Since 2015, a board of inquiry set up by the Polish government has been conducting its own investigation of the case: the victims' remains are being exhumed and checked for evidence of explosives.

Former minister called to the witness stand

On Tuesday, Tusk's then-foreign minister Radoslaw Sikorski will give testimony as a witness in another trial that deals with alleged neglected duties on the part of Polish diplomats in connection with the Smolensk crash.

In addition, Polish authorities are now leveling accusations against the Russian air traffic controllers: In heavy fog, they allege, they deliberately "lured" the Polish plane into disaster. The motive was, according to their logic, to get rid of Lech Kaczynski, who had always been a vociferous critic of the Russia's then-prime minster and current president, Vladimir Putin.

A wreath for his brother: Jaroslaw Kaczynski attending the Warsaw memorial ceremony

Thus far, radio communication recordings have revealed that the two air traffic controllers on duty at the rarely used forest airfield near Smolensk had been hopelessly out of their depth. They telephoned their superiors for advice and ultimately decided - despite the dense fog - to give the presidential plane permission to land instead of blocking the airfield. The allegation is now that the implicated persons "deliberately" caused the crash.

The Smolensk probe divides the country to this day, giving rise to the term "Smolensk religion." The incident is also being used for domestic policy purposes: by allocating the blame to various quarters, the governing PiS party wants to attribute a political motive to the tragic event, thereby aligning it with earlier national tragedies - Katyn, for instance.