"The moment that - that thing entered the room, it swooped down on Crouch and - and -"
-- Minerva McGonagall, screaming about what Fudge had done (GF36)
Cornelius Fudge takes a Dementor with him into Hogwarts as protection. When the Dementor gets near to Barty Crouch Jr., it attacks and administers the Kiss. Fudge sees no great loss, but Dumbledore realizes this means they have no proof that Voldemort has returned. This moment is the beginning of the parting of the ways between the two.
Curious that the Dementor immediately attacked Crouch. What attracted that loathsome creature to Crouch anyway? Did it sense deep betrayal and evil? Or did Fudge sense a threat to his position and decide to dispose of Crouch before his testimony started rumors of Voldemort's return?