[Obi-Wan didn't have to see the films. He found the bodies.]

"Anakin, in the timeline I came from... Palpatine had gone a step farther. He confessed to you that he was a Sith Lord, and you reported it to Master Windu. When Master Windu attempted to arrest him, he attacked and killed Windu. He told the Senate it was an assassination attempt...

And he used the public sympathy to gain the approval he needed to reform the Republic into an Empire. He made himself an Emperor, Anakin."