McCabe's lawyer got the final report from the OPR, not the OIG.
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Assistance of Counsel
The majority of OPR investigations are administrative in nature, and employees are not en led to counsel as a matter of law. However, counsel may be permitted if counsel does not interfere with or delay the interview. Counsel must be actually retained by the employee as his legal representative, not as an observer. Counsel are not permitted access to certain confidential criminal investigative information and may not be permitted access to grand jury information.
Post Investigation Procedures
At the conclusion of the investigation, OPR prepares a report of investigation in which it makes findings of fact and reaches conclusions as to whether the subject attorney committed professional misconduct. OPR may find the subject attorney committed professional misconduct by: (1) intentionally violating a clear and unambiguous obligation or standard imposed by law, applicable rule of professional conduct, or Department regulation or policy; or (2) recklessly disregarding his obligation to comply with that obligation or standard. OPR may also find that the attorney exercised poor judgment or made a mistake. A poor judgment finding may lead to disciplinary action; a mistake finding does not.
Once OPR completes its report of investigation, the subject attorney and the component head are officially notified of the results of the investigation. If OPR determines that the subject attorney committed professional misconduct, prior to issuing a final report, the subject attorney, pursuant to a confidentiality agreement, and the component head may review the draft report, comment on the factual findings, and offer arguments as to why OPR should alter its conclusions. OPR will consider the comments and incorporate them into the final report, to the extent OPR considers it appropriate.
OPR may include in its report information relating to management and policy issues noted in the course of the investigation for consideration by Department officials.
Pursuant to 28 C.F.R. § 0.39a and OPR's routine uses under the Privacy Act, OPR also notifies the complainant of the results of the investigation.
https://www.justice.gov/opr/policies-and-procedures#7