When a tube traveller turned on four men he thought were robbing him, and shot them, he also fired one of the most intense debates on crime in America this century. The implications of that one act have continued to reverberate and widen into deeper issues of vigilantism and racism. Tom Mangold rides with TONY IMPERIALE 'S white vigilantes and with the undercover cops in an investigation into the uncomfortable truth now emerging from the case of the 'subway vigilante'