A 15-month investigation by Dutch authorities into doomed Malaysia Airlines Flight 17 has determined a Russian-made missile shot the plane down over Ukraine and killed all 298 people on board.

The findings by the Dutch Safety Board will be unveiled Tuesday, according to a report from The Sunday Times of London.

Dutch investigators studied shrapnel from the July 17, 2014, crash, plus statements from separatists, images of a Buk missile launcher in the area and intelligence phone records.

They concluded that separatist rebels, using weapons provided by Russia, hit the Boeing 777, believing it to be a Ukrainian warplane.

“Of course, people will always be able to speculate, but our report will provide all the factual evidence, and we are pretty confident in our conclusions,” a source close to the investigation told The Sunday Times.

However, Almaz-Antey, the manufacturer of Buk missiles, says it will announce the “real reason” for the crash on the same day the Dutch report is released.