One of the eeriest pieces of evidence emerged last year and was highlighted again on Wednesday. The pilots had no chance of saving the plane, and were perhaps the first to die, because the missile exploded yards from the cockpit. But one carried to earth in his body a pivotal clue: a butterfly-shaped piece of shrapnel, a trace from a type of warhead installed in Buk missiles in Russia’s arsenal, but not Ukraine’s. Both countries possess Buk missiles, but the model types are distinct.

It would have been a hard piece of evidence to fake. Plastered onto the shrapnel shard, investigators said, were microscopic traces of glass of the type used by Boeing on its airliner cockpits, indicating clearly that it had passed through the plane’s windshield before lodging in the pilot’s body.

In Moscow on Wednesday, in anticipation of the report, President Vladimir V. Putin’s spokesman, Dmitri S. Peskov, issued a statement to reporters decrying “speculation” about the plane, but it did not refer specifically to the report.

“This whole story, unfortunately, is couched in a huge amount of speculation, unqualified and unprofessional information,” Mr. Peskov said. “There are irrefutable facts. In this case, it is important to draw conclusions with due account of the latest published information, that is, the primary data from radars that detected every airborne object that could take off or be in the airspace above militia-controlled territory.”

Those radar images, released by the Russian military on Monday, showed nothing near the airliner, Mr. Peskov said. “If any missile had existed, it could have been fired only from another territory,” he said. “I do not say which exact territory it could be. It is specialists’ business.”

The Dutch-led inquiry seemed to refute that claim, as well as a series of sometimes contradictory explanations and chains of events floated by the Kremlin and the Russian news media. Those claims included that the C.I.A. filled a drone with bodies and crashed it to discredit Russia, or that Ukrainians were trying to shoot down Mr. Putin’s plane but hit the civilian airliner instead.

The radar images released this week contradicted a similar image that Russian officials showed two years ago, which depicted two dots: one for the airliner and a second for a Ukrainian fighter jet that Russia suggested could have shot it down. At the news conference, the investigators said Russia had not responded to their request for “primary original radar data.”