Any person may be compelled to testify in any lawful proceeding against another charged with commercial bribery, public bribery, bribery of voters or corrupt influencing, and shall not be permitted to withhold his testimony upon the ground that it may incriminate him or expose him to public infamy; but such testimony shall not afterwards be used against him in any judicial proceeding, except for perjury in giving such testimony.
La. R.S. § 15:468