No person called as a witness in any prosecution or proceeding to enforce the antitrust laws of this state, though himself a defendant therein, or an officer, attorney, agent or employee of a defendant or stockholder in a defendant corporation, shall be excused from testifying upon the ground that his evidence might criminate or tend to criminate himself; but every person, otherwise competent, when called as a witness in such cases, shall be required to testify and to disclose all facts known to him which are pertinent to the issue.