t incriminate witness for crimes he had already committed, or was in process of committing, at time testimony was given. U.S.C.A. Const.Amend. 5. Roger M. Olsen, Atty. Gen., Michael L. Paup, Chief, Robert E. Lindeay, Alan Hechtkopf, Appellate Section, Tax Division, U.S. Dept. of Justice, Washington, D.C.,