He presented himself as a master of the deft bureaucratic maneuver, both in his dealings with internal family rifts and with other crime clans, and in his efforts to thwart law enforcement.

He described going to the bosses of the Gambino and Colombo families — Paul Castellano and Carmine Persico, respectively — in 1981 before taking pre-emptive action against three senior Bonanno figures who were moving against his faction in a brewing power struggle. After securing approval to kill the men, Mr. Massino and several others shot them to death in an ambush in the basement of a social club.

He also testified about codes that he and his confederates worked out — to discuss murder plots and in one instance to determine if a social club had been bugged — without alerting law enforcement. He described changes he put into effect after becoming boss that were meant to reduce the risk that members of his family could incriminate themselves or one another.

For example, Mr. Massino closed all the family’s social clubs, saying that if crime family members hung out in these storefront establishments, they made the Federal Bureau of Investigation’s job easy, because one agent conducting surveillance outside could see everyone come and go. “If you close the club,” he explained, “it takes 50 F.B.I. agents to watch 50 people.”

He was, he said, extremely careful about where and when he talked about mob business.

“You never talk in a club, you never talk in a car, you never talk on a cellphone, you never talk on a phone, you never talk in your house,” he testified, saying that so called walk-talks, where two or more crime figures would carry on a roving conversation as they strolled the streets, were safest.

Indeed, Mr. Massino said he discussed mob business in a walk-in refrigerator at a catering business where he worked to avoid electronic eavesdropping.

His efforts to thwart investigators, he said, were aided by at least four unnamed law officers: two New York Police Department detectives in the 1960s; an F.B.I. agent who warned him of a pending arrest in the 1980s; and a Pennsylvania state trooper who destroyed copies of his fingerprints sometime later.