In order to facilitate the making of investigations by the Department, in the interest of public safety and promotion of aeronautics, the public interest requires, and it is, therefore, provided that the reports of investigations or hearings, or any part thereof, shall not be admitted in evidence or used for any purpose in any suit, action or proceeding, growing out of any matter referred to in the investigation, hearing or report thereof, except in case of criminal or other proceedings instituted in behalf of the Department or this State under the provisions of this chapter and other laws of this State relating to aeronautics, nor shall the Secretary of Transportation, or any officer or employee of the Department be required to testify to any facts ascertained in, or information gained by reason of, his official capacity, or be required to testify as an expert witness in any suit, action or proceeding involving any aircraft. Subject to the foregoing provisions, the Department may make available to appropriate federal and state agencies information and material developed in the course of its hearings and investigations.