Poland has commemorated the 11th anniversary of a plane crash near the Russian city of Smolensk that killed 96 people — including Poland’s then-President Lech Kaczynski, his wife, and many of the country’s senior political and military officials.

Many Poles, including senior members of the governing Law and Justice Party, question the results of an investigation released in 2011 by a special Polish commission.

It concluded the Tu-154 military flight from Warsaw had crashed on April 10, 2010, in extreme fog on its approach to an airport near Smolensk because of pilot error and a lack of warnings from Smolensk air-traffic controllers.

Poles are also suspicious of Russia’s handling of the investigation.

The current Polish president, Andrzej Duda, has noted that while Russia turned over data from the plane’s flight recorders that it deemed relevant to the case, “the wreckage is still in Russia; the black boxes are still in Russia.”

The late president’s twin brother, Jaroslaw Kaczynski, has said he suspects the crash was the result of an assassination plot by the Russians.

The tragedy has strained relations with Russia, all the more so because the plane had been traveling to commemorate the World War II Katyn massacre of some 22,000 Polish military officers and civilian intelligentsia by Soviet secret police.

Events commemorating the plane crash on April 10 began in the morning with a Roman Catholic religious service and the laying of wreaths at a monument dedicated to the victims of the crash and at their graves.

An evening religious service was also scheduled in a Warsaw cathedral.

For the second consecutive year, the commemorations took place amid coronavirus restrictions and were limited in scope.

Prime Minister Mateusz Morawiecki described the crash in a Facebook post on April 10 as “the biggest national tragedy in Poland’s postwar history.”

With reporting by Reuters, AP, AFP, and dpa