Long before the murder, the girls and a role in “The Godfather,” Gianni Russo was a 13-year-old with a bum arm. Freshly sprung from Bellevue’s polio ward, he ditched his neglectful parents to sleep on flour sacks in the back of a Little Italy bakery and sell pens in front of the Waldorf-Astoria. It was 1956 and one of his regular customers was mob boss Frank Costello. The don would throw Russo a fiver and rub the boy’s withered shoulder for luck. After a few months of that, Russo objected to being touched. Costello respected the kid’s gumption — and...