For the purpose of all hearings and investigations which in the opinion of the Commissioner are necessary and proper for the exercise of the powers vested in him, the Commissioner shall at all reasonable times have access to, and for the purpose of examination, the right to copy any evidence of any person being investigated that relates to any matter under investigation. The Commissioner may issue subpoenas requiring the attendance and testimony of witnesses and the production of any evidence that relates to any matter under investigation or in question, before him. He may administer oaths and affirmations, examine witnesses and receive evidence.