The White House on Tuesday came close to declaring that the Kremlin was responsible for the death of Wagner mercenary group chief Yevgeny Prigozhin, who was believed to have been killed in a mysterious plane crash last week.

“We all know that the Kremlin has a long history of killing opponents,” said White House press secretary Karine Jean-Pierre. “It’s very clear what happened here.”

Her comment was the closest US statement yet on the possibility that Russian President Vladimir Putin directed the killing of Prigozhin, who had launched a brief mutiny against the Kremlin in June.

Prigozhin was killed last week when the plane was he flying in abruptly crashed outside of Moscow. Theories have abounded on what brought the plane down, from an explosion on board to a surface-to-air missile strike.

US President Joe Biden told reporters last week that the United States was working to try to reach a conclusion on how the plane was brought down. “We’re trying to nail (it) down precisely,” he said on Friday.

Biden also said it was no surprise that Prigozhin had been killed after opposing Putin.