code of silence

小説のStill Aliceは読み終わりましたが、巻末に付録として 'A Conversation with Lisa Genova' があり、そこから引用します。
"So which one of you did this?"
They all stare and say nothing. The Charlestown code of silence, eh?
"Who picked up my gun and left it by the sink?" he demands, his voice booming. Silence will not be an option.
"code of silence" とは何でしょう？ 英英辞書でこの項を掲載しているものは見つかりませんでしたがWikipediaに次の説明がありました。
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 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. 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.
なるほど、日本の警察にも、いや警察だけではなく、役所、政党、企業など仲間内の不祥事やら悪い行いを隠していることが多々ありますが、最近は内部告発のせいか色々と驚く程の不正行動が明るみに出てきていますね。
上の説明に出てきた警察による "Blue Code of Silence" についてのWikipediaの説明もついでに引用します。
Blue Code of Silence: The blue wall of silence, also blue code and blue shield, are terms used in the United States to denote the informal rule that purportedly exists among police officers not to report on a colleague's errors, misconducts, or crimes, including police brutality. If questioned about an incident of alleged misconduct involving another officer (e.g. during the course of an official inquiry), while following the code, the officer being questioned would claim ignorance of another officer's wrongdoing or claim to have not seen anything.