Wagner mercenary group chief Yevgeny Prigozhin’s death in a plane crash last week was confirmed by Russian investigators, as speculation over a possible Kremlin-ordered execution continues to swirl.

DNA tests showed that all 10 passengers and crew listed as having boarded the private jet on Aug. 23 were killed, according to a statement on the Russian Investigative Committee’s website Sunday.

Prigozhin led a failed mutiny in June against Vladimir Putin’s military leaders that threatened the Russian president’s nearly quarter-century grip on power. The U.S. has said the plane crash may have been an assassination approved by Putin himself, suggestions that the president’s spokesman Dmitry Peskov dismissed as "an absolute lie.”