On the night of Mr. Melvyn's murder, Little Johnny was on his way home from Cuban Pete's taekwondo class.    He saw his homeboy, Yo-Danny, on the streetcorner just hanging out. "Yo", said Johnny, "wassup?". Yo-Danny said nothing - he was too busy staring at a man dressed in a trenchcoat who was dragging a half-naked skinny type out of the gay club across the street, the Boom Boom Bar.