For nearly a decade, families visited a small coffee shop in suburban Long Island for pastries and gelato. Many were unaware of the longstanding operation playing out just feet away from them: Mafia members were running a secret underground gambling den in the store.

The business was one of several across the island and in Queens that served as a front for two of New York’s oldest crime families and their illegal moneymaking schemes, according to two federal indictments unsealed Tuesday. When other gambling clubs threatened their fortunes, an active Nassau County detective offered to conduct police raids on them, in exchange for payments, prosecutors said.