In an interview with Tom Brokaw of NBC, Secretary of State John Kerry said he has “serious doubts” that Lee Harvey Oswald, who assassinated President John F. Kennedy, acted alone.

The Warren Commission, which investigated the assassination, came to the opposite conclusion. The commission did suggest, however, that Oswald’s motive for murdering Kennedy might have arisen from Oswald’s “avowed commitment to Marxism and communism.”

“Where do you come down on the conspiracy theories?” Brokaw asked Kerry in a clip from the interview that was broadcast on CNN’s “Situation Room” on Friday.

“To this day, I have serious doubts that Lee Harvey Oswald acted alone,” said Kerry.

“Really,” said Brokaw.