That dialogue is in the shooting script but it didnt make the final cut. What could the Jedi have done to find out about the Sith? The dark side is hard to see. The Sith were yet to reveal themselves. There isnt enough screen time to show the Jedi going about usual investigative stuff. We should just assume that they do. Just because we cant see something, doesnt mean it does not exist! IMO, the Jedi must think the Sith had been around in hidding for a millenia. They believe it is the Sith of old whom have returned. The Sith is someone who lives by the doctrines of the Sith Order. Knowledge is passed down. Thats what the Jedi think has happened IMO. [quoteNordom]Since Sifo-Dyas is dead the jedi would have no way of knowing if he had turned to the dark side or not. All they know is that he went behind the senates back and behind the jedi councils back as well to create a clone army.[/quote] We dont know that. Like i said, there is proof of initial contact - not that he ordered the clones. I personally think Sidious/Dooku did that in his name. I think Sifo was checking things out and would have made that aware to the Jedi. Probably a big reason why Dooku killed him. Indeed. But they trusted Palpatine and the Senate. That was a mistake.