Salvatore "Sammy the Bull" Gravano (born March 12, 1945) is a former underboss of the Gambino crime family. He is known as the man who helped bring down John Gotti, the family's boss, by agreeing to testify against him and other mobsters in a deal in which he confessed to involvement in 19 murders.
He also testified against other mobsters along with Gotti
The context states that he agreed "to testify against him (Gotti) and other mobsters". I wrote "He also testified against other mobsters along with Gotti" which is the same statement but reversed. Not sure why the AI didn't catch it, but it is correct.