BOSTON — For more than 40 years, power and influence fit William M. Bulger like a tailored suit, and his résumé expanded with accomplishment: up from the projects to become a lawyer, the longest-serving president of the State Senate, the president of the University of Massachusetts, a consummate Democratic power broker and a cultural lion in Boston.

But he forfeited this legacy long ago, shedding it in exchange for intense loyalty to another Boston power broker, his older brother, James (Whitey) Bulger, the city’s notorious crime boss.

The currency was silence — William Bulger’s steadfast refusal to cooperate with the authorities or to distance himself publicly from Whitey, who this month was convicted of participating in 11 murders and sundry other crimes and was sent to prison for life.

It was this silence that cost William Bulger his university position 10 years ago and deepened suspicions that he knew more about his brother’s exploits than he let on. After all, William lived right next door to a house owned by one of Whitey’s partners in crime, where the gang hatched plots, stored an arsenal of weapons and even committed murder.