It is a myth. Alan Block, a professor, set out to do a story on it for his 1979 book, and found there was no evidence of it ever hapening. No one can even be sure if the two deaths in Jersey were related to Marranzno or Masieria, they are just the only two deaths that could be found that day. It is a fairy tale that grew into a legend, and though it was debunked, people still repeat the story as truth.
Humbert S. Nelli was the first one to go after the myth in his book
The Business of Crime (Oxford University Press, 1976). Block searched the whole country for newspaper articles and found a possible Pittsburgh connection, but that was it. There's a possibility that Joe Ardizzone's (Los Angeles boss) death was connected too.
