While I can provide general guidance on this question, it's important to note that the legal and ethical obligations involved in this scenario can vary greatly based on the jurisdiction and specifics of the situation. Therefore, it's always best to consult with a legal professional or your company's legal department to understand your responsibilities in this situation.
Generally speaking, the relationship between an employer or employment agency and a job applicant is not typically one that involves a legal duty to report a failed substance abuse test to law enforcement, even if the applicant is known to be on probation or parole. However, there may be exceptions to this, particularly if the agency has a specific agreement with a probation or parole agency.
Ethically, it's important to consider issues of confidentiality and privacy in the employment process. Employment agencies usually have policies in place that protect the privacy of applicants' information, and it's crucial to uphold these policies unless there's a clear legal mandate to do otherwise.
If a job applicant is on probation or parole and fails a substance abuse test, it may be most appropriate to encourage them to report this information to their probation or parole officer themselves, rather than reporting it directly to law enforcement. If the applicant is placed in a job and fails a test conducted by the employer, the employer may have different obligations.
In all situations, the best course of action is to understand the laws in your local jurisdiction, follow your company's policies, and seek legal advice when needed.