The criminal tax statutes used in most cases involve tax evasion, false returns, failure to file a return or to pay tax, and miscellaneous tax crimes including, interalia, aiding and abetting, conspiracy, false statements, and false claims. The most essential and difficult to prove piece of evidence needed by the government is that the defendant actually owed more taxes than were paid. The four main methods of proof that have gained judicial approval are the specific items method, the net worth method, the expenditures method, and the bank deposits method. The discussion of defense preparation for criminal tax cases covers the criminal tax investigation itself, the period between investigation and indictment, and the period from indictment to judgment. Post-conviction advocacy is often guided by the principle of collateral estoppel which refers to the Internal Revenue Code provision for numerous civil penalties against the offender. 301 notes.