Code of silence; not be mistaken
A Code of Silence is when a person opts to withhold what is believed to be vital or important information voluntarily or involuntarily.
The code of silence is usually either kept 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 experiences of the police whistleblower, Frank Serpico illustrates. The Code of Silence was famously practiced in Massachusetts cities such as Charlestown, South Boston, and Somerville.
A more famous example of the code of silence is omerta (Italian: omertà , from the Latin: humilitas=humility or modesty), the Mafia code of silence.
Sometimes, this phrase is mistaken with a cone of silence.