WARSAW (AFP) - Three years after a jet crash in Russia killed a Polish president and 95 other people, conspiracy theorists in Poland are as adamant as ever that it was an assassination.
The conservative opposition - led by the late Lech Kaczynski's twin brother Jaroslaw - has accused leaders from Warsaw and Moscow alike of having a hand in the crash on April 10, 2010.
Many high-profile Poles died when the Russian-made Tu-154 airliner went down in thick fog while approaching Smolensk airport in western Russia.
The delegation was en route to memorial ceremonies in Katyn for thousands of Polish army officers slain by the Soviet secret police in 1940, a massacre the Kremlin denied until 1990.
Poland's conservative Law and Justice (PiS) party has repeatedly accused Prime Minister Donald Tusk's centre-right government of not taking Russia to task over what it insists was a botched investigation and cover-up.
Fuelling the fire is Moscow's foot-dragging on handing over the wreckage to Poland, where around 30 percent of the population are PiS supporters.
For the Wednesday anniversary, the party has called for demonstrations at the Russian embassy and the presidential palace in Warsaw and will release a fresh report on the crash.
A Russian probe concluded in 2011 that the crew was under "psychological pressure" to land in dangerous weather, a report Warsaw slammed as incomplete and riddled with errors.
A Polish report attributed the crash to errors by the ill-trained crew, mostly blaming Poland but also faulting Russia for the sub-standard airfield and poor traffic control there.
But it unequivocally ruled out "extremist versions" of events, including sabotage and third-party pressure on the crew to land despite bad weather.
Three Polish generals and 10 other senior officers were sacked, while the military unit responsible for flying public officials was dissolved and civilian pilots took over its duties.
But neither the probes nor the purges have convinced Antoni Macierewicz, a conservative PiS legislator and close Kaczynski ally.
His parliamentary working group concluded the crash was an assassination masterminded by Tusk - the Kaczynski twins' arch political rival - and Russian President Vladimir Putin, who was prime minister at the time.
"The latest studies reinforce our conviction that the catastrophe followed explosions," Macierewicz said in a report to be published Wednesday.
The analysis ignores that Polish prosecutors concluded that no explosive traces were found on the wreck.
Mr Macierewicz alleges that a tune-up in Russia on the ill-fated jet not long before the crash had been "managed by Russian intelligence services", while "Donald Tusk and Vladimir Putin were playing a game against president Kaczynski".
Thirty-three percent of Poles said they "would not exclude" the possibility of an assassination, according to a survey published last month.
The result sent the Tusk government - which had long viewed such allegations as the ravings of a lunatic fringe - scrambling to form a group of experts to refute the conspiracy theories one by one.
The deep political rift in Poland over the crash is likely to remain an issue during the 2015 presidential and parliamentary elections, says historian Antoni Dudek.
Tusk has also taken a harder line with Moscow on the issue, accusing it in January of "ill will" because of delays in handing over the jet wreckage.
Foreign Minister Radoslaw Sikorski charged Moscow with trying to stir up trouble among Poles, and asked EU foreign policy chief Catherine Ashton to convince the Russians to return the wreckage.
Moscow has since promised it will upon completing its probe.