There is an area of common law which applies to employment...actually two areas...wrongful discharge and defamation.  Defamation cases involve statements made by an employer, which can't be documented, which impede previous employees ability to find replacement employment.  For example, one previous employer was found liable when he/she told a potential employer who called for a background check, that the previous employee "suddenly resigned."  The court reasoned that the phrase "suddenly resigned" had negative connotations making it difficult for the previous employee to find another job.  It seems to me that a phrase like "may have committed illegal actions" might be defamation too when made by a current or previous employer, assuming it can't be documented.