In the United States v. Townsley case of 1944, the Supreme Court ruled on a matter concerning federal income tax evasion. The defendant, Mr. Townsley, was accused of evading taxes by not reporting his full income from oil royalties and other sources for several years in the late 1920s and early 1930s. He argued that he had been advised by his accountant to report only net profits rather than gross receipts as taxable income which led to underreporting of his earnings. The court held that even if this advice were true, it did not excuse him from knowingly filing false returns or absolve him from criminal liability for tax evasion because ignorance of law is no defense against violation thereof (actus reus non facit reum nisi mens sit rea). Furthermore, they stated that there was sufficient evidence presented at trial showing intent to defraud government revenue. This ruling reinforced two important principles: first, taxpayers are responsible for accurately reporting their incomes regardless of any incorrect advice they may receive; secondly, demonstrating an intention to evade taxes can be enough grounds for conviction even without direct proof such as written documents or explicit statements.

In the dissenting opinion for United States v. Townsley, Justice Frank Murphy argued that the majority's decision to uphold a conviction based on evidence obtained through wiretapping was fundamentally flawed. He contended that such methods of obtaining evidence were in direct violation of an individual's right to privacy as protected by the Fourth Amendment and should therefore be deemed unconstitutional. Furthermore, he asserted that allowing this type of surveillance would set a dangerous precedent, potentially leading to widespread abuses of power by law enforcement agencies. In his view, it was essential for courts to safeguard citizens' constitutional rights rather than facilitating their erosion in the name of crime prevention or national security.