He knows the ways of the Force. He's been trained to use the dark side.
7 seconds sound clip from the Star Wars: Episode III - Revenge of the Sith movie soundboard.
You can hear this line at 01:08:04 in the Blu-ray version of the movie.
Quote context
[...]
- Skywalker. We just received word that Obi-Wan has destroyed General Grievous.
- We're on our way to make sure the chancellor returns emergency power back to the senate.
- Yes. The one we've been looking for.
- He knows the ways of the Force. He's been trained to use the dark side.
- Then our worst fears have been realized.
- We must move quickly if the Jedi order is to survive.
- Master, the chancellor is very powerful. You'll need my help if you're going to arrest him.
[...]