Rene Enriquez was a leader in one of America's most violent gangs, the Mexican Mafia.
He is serving 20 years to life in California for murders he committed for the gang.
While in prison, Enriquez rose to a powerful position in the Mexican Mafia.
But then he had a change of heart.
Michael Montgomery reveals extraordinary recordings made by Rene Enriquez in prison, which chart his progress from gang member to police informant.
BBC Radio 4's Crossing Continents was broadcast on Thursday, 11 September, 2008 at 1102 BST.
Reporter: Michael Montgomery from American Radio Works
Producer: Anna Raphael