Here is an account of the boxer's untimely death . http://www.boxinggyms.com/news/brennan1924herald/brennan1924herald.htm
Quite a tragic episode when you consider that Brennan had only recently retired from the ring. I'm not sure if it was ever proven to be a bootlegging-related murder or just something pointless and spiteful. Either way, obviously he upset the wrong people. One of Brennan's killers, Joseph Pioli (who may have been the same person as Frank Rassi or Frank Rossi in the initial arrest reports) later broke out of Sing Sing prison in 1927 and was on the lam for two years.
