He was convicted and sentenced to 30 years. Then the prosecutor approached him with a deal to knock half of that time off in return for testimony against Knox and Sollecito.
Not quite. He was called to testify, but asserted his right to say nothing (as he has all along).
Knox and Sollecito were charged before his involvment was known, and convicted without testimony from him.
Rudy Hermann Guede: Amanda Knox And Ex-Boyfriend Are The Killers
PERUGIA, Italy — A man convicted of murdering a British exchange student testified Monday that he believes her roommate, Amanda Knox, and her ex-boyfriend killed her – an accusation that prompted an emotional denial from Knox.