Most criminal tax cases start with civil audits.
Per Title 26 §7206: Any Person who… (1) Declaration under penalties of perjury - Willfully makes and subscribes any return, statement, or other document, which contains or is verified by a written declaration that is made under the penalties of perjury, and which he does not believe to be true and correct as to every material matter; shall be guilty of a felony and, upon conviction thereof;
Elements Necessary for Prosecution:
(1) Making and subscribing a return or other document under penalties of perjury
(2) The return, statement or other document, which was false as to a material matter
(3) Belief that it is not true and correct as to every material matter