Code of silence

A code of silence is a condition in effect when a person opts to withhold what is believed to be vital or important information voluntarily or involuntarily.
The code of silence is usually followed because of threat of force or danger to oneself, or being branded as a traitor or an outcast within the unit or organization, as the experience of police whistleblower Frank Serpico illustrates. Police are known to have a well-developed Blue Code of Silence. The code of silence was famously practiced in Irish-American neighborhoods in Boston, Massachusetts such as Charlestown, South Boston, and Somerville.
A more well-known example of the code of silence is omertà (Italian: omertà, from the Latin: humilitas=humility or modesty), the Mafia code of silence.