Dooku and Sidious wished Sifo-Dyas dead in order to take control of the clone army Sifo-Dyas had secretly ordered from the cloners of the remote planet Kamino, as he had foreseen a war coming that would require the Galactic Republic to have an army. Dooku then travelled to Felucia with the body, deceiving the tribal elders into thinking that Sifo-Dyas was still alive and that he was another Jedi who had accompanied him. The Sith Lord then faked Sifo-Dyas' death in the conflict and had his body cremated.
The Jedi Council believed Sifo-Dyas had died on Felucia until the last year of the Clone Wars, when the wreckage of Sifo-Dyas' ship was uncovered on the Oba Diah moon, with his lightsaber still inside — clear proof that he could not have perished on Felucia. Anakin Skywalker and Obi-Wan Kenobi were sent to speak with the Pykes, and discovered the true circumstances of Sifo-Dyas' death and that the Sith had been responsible.
The mission to Felucia was first mentioned in the Star Wars: The Clone Wars episode "The Lost One."