whistleblower

/ˈwɪsəl ˌbloʊər/
noun
  1. A person who tells the public or someone in authority about dishonest or illegal activities within an organization.
    • The whistleblower provided documents that proved the fraud.
    • The company's whistleblower was awarded a percentage of the money recovered.
    • Many whistleblowers face retaliation, but laws exist to protect them.