Caution Major Film Spoilers -------------------------------------------------------------------------------- Fudge, Dumbledore and Umbridge at Harry's trial.
Umbridge did not send he dementors. As implied by Dumbledore's reply, he does not mean to suggest that the ministry had anything to do with it. Hense "without authorisasion... "of course there is someone who might be behind the attack... the evidence of the dark lords return..." It is clear that Dumbledore believes that the attack was instigated by Voldemort directly or indirectly.
LOL I misstyped. Umbridge DID sent them, as she confessed later on in the book to Harry himself. I was simply trying to point out that at the time Dumbledore himself did not seem to have come to that conclusion at the time. It is clear that Dubledore was implying that the Dark Lord was the reason the dementors were there. In reality, yes, it was Umbridge doing it for the sake of the ministry.
