If Father Bobby had decided not to testify, King Benny probably...
...could have come up with a witness pretty quickly to testify they were with John and Tommy the night of the killing instead.
Local gangster bosses like King Benny in New York usually have a list of crooked cops, and King Benny whose own nephew was a cop (supposedly an honest one) certainly would have, so all King Benny would have had to do was to run down his list of crooked cops, find one who they could cook up a credible story that they would have known John and Tommy -- it is really not that unusual for young cops to know some of the hoodlums they end up arresting as semi-friends -- and were off duty the night of the basketball game.
Then they could have the crooked cop use the same story they used for Father Bobby -- "I bought the tickets for cash, I met up with the guys at about 6:30, we went to the game, it got out about 10, they went home" -- and even have him keep the ticket stubs too to 'prove' it.
The story that a young cop in his 20s would hang around with 2 guys who were street thugs is really no more far-fetched than a priest would suddenly decide to go to a basketball game with 2 street thugs who used to go to his parish 15 years ago.
In either case, the jury would have either the word of a priest -- or a cop -- to support the story that John and Tommy had gone to the basketball game.
Either way that's enough to counterbalance the testimony of the semi-drunk housewife.
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4) You ever seen Superman $#$# his pants? Case closed.