In furtherance of the policy and purposes of this chapter, the Secretary may make or cause to be made any investigation or study which is, in his or her opinion, necessary for the purpose of enforcing this chapter. For such purposes the investigative officer designated by the Secretary may subpoena witnesses and the production of documents and compel their testimony. Testimony received at a Departmental investigation shall be under oath and open to the public. Findings of these investigations or studies shall be made public.