Russia handed Poland's top military prosecutor on Thursday thousands of pages of evidence on the plane crash in April that killed Polish President Lech Kaczynski and 95 other people.
Among the materials passed to Gen Krzysztof Parulski were interviews with witnesses of the crash, documents referring to mobile phone video of its immediate aftermath made by local residents, photographs taken at the scene and forensic evidence from body parts.
"Everything the Polish side is requesting, we are providing," said Deputy Prosecutor General Alexander Zvyagintsev.
Russian authorities have blamed heavy fog and pilot error for the crash in Smolensk, in western Russia, which wiped out much of Poland's civilian and military leadership. Initial black box recordings showed there were unauthorized personnel on the flight deck before the disaster.
Zvyagintsev said this was the second hand-over of investigative material. The first was in June and the next is likely to come soon, he said.
Parulski thanked the Russians for their work, and suggested that accusations by some Polish politicians that Russia was dragging its feet in providing evidence was unfounded.
"I would like to give my thanks for this huge volume of material," he said.
Polish officials complained earlier this month about what they said was Russian procrastination in handing over evidence, crucial for Poland's own investigation into whether anyone in Poland is to blame. The Polish investigation is being conducted alongside the main Russian investigation, in which a Polish official is an observer. Each side is supposed to share information with the other.
Polish Interior Minister Jerzy Miller said holes in the documentation provided by Russia were preventing the Poles from reaching conclusions. Prime Minister Donald Tusk said he would ask Moscow for an explanation of the delays in making the documents available.