Who turned in john gotti?

John Gotti was turned in by Salvatore "Sammy the Bull" Gravano, his underboss in the Gambino crime family. Gravano agreed to cooperate with the government after being indicted on multiple charges, providing crucial testimony that led to Gotti's conviction in 1992. Gravano's testimony exposed Gotti's criminal activities and ultimately contributed to Gotti's life sentence in prison.