Russia's state archives has posted to the internet for the first time documents about the Soviet Union's Second World War massacre of more than 20,000 Polish officers and other prominent citizens.
The step was a gesture to Poland in a case that looms large in the country's history and has soured relations between the two countries for decades.
President Dmitry Medvedev ordered the documents posted on the archives' website, reflecting a new willingness in Russia to accept responsibility for the killings at Katyn and elsewhere in 1940.
Relations between Russia and Poland have warmed since April 10, when Polish President Lech Kaczynski, his wife and 94 others were killed in a plane crash on their way to the Katyn forest in western Russia for a memorial ceremony on the 70th anniversary of the massacre.
But while Medvedev's order was clearly intended as a positive gesture, the documents posted Wednesday were made public long ago, and have already been published in Poland and Russia. Many more documents remain classified, despite dogged Polish appeals for the archives to be opened.
Documents already public
The documents now on the internet were made public in 1992 by Boris Yeltsin, Russia's first post-Soviet leader. They include a March 1940 letter by Lavrenty Beria, head of the secret police, recommending the execution of the Polish prisoners of war. The letter bears the signatures of Soviet dictator Josef Stalin and three other members of the Politburo.
The documents also include the minutes of a Politburo meeting on March 5, 1940, and a note from the head of the Soviet secret police in 1959 informing Soviet leader Nikita Khrushchev that the Katyn files had been destroyed.
For 50 years, the Soviet Union blamed the massacres on the Nazi German forces that invaded in 1941. This remained the official line until Soviet leader Mikhail Gorbachev acknowledged Soviet responsibility in 1990, but Poles had always known the truth and the coverup fed animosity toward Russia.
Documents that remain classified include materials from an investigation in the 1990s that are believed to include the names of those who carried out the executions.
Russia also has refused Polish requests to recognize the executed Poles as victims of political repression.
Polish historian Andrzej Kunert said although the documents posted Wednesday were known to historians, the decision to post them on the internet was significant.
"We can surely call the decision a breakthrough, because it seems that for the first time a website that is generally accessible to everyone in the Russian Federation publishes three very important documents concerning the Katyn massacre," Kunert said on Polish TVN24. "It is certainly a very important step forward."
Many Russians still do not know the truth about Katyn, and the release of the documents may play a positive role in helping Russians come to terms with their own painful history under Stalin.
Within hours of the posting of the documents, nearly 700,000 internet users tried to access the website, the ITAR-Tass news agency reported, citing a spokesman for the state archives. The website was responding slowly due to the heavy traffic.