In the 1993 case of Harold E. Staples, III v. United States, the Supreme Court ruled that a defendant's lack of knowledge about certain characteristics of an object in his possession does not exempt him from prosecution under federal law if those characteristics make the object a firearm subject to regulation and registration requirements. The case involved Mr. Staples who was found guilty for possessing an unregistered machine gun contrary to federal law after police discovered he owned a modified semi-automatic rifle capable of automatic fire during a search at his home for unrelated reasons. He appealed on grounds that he was unaware it could be fired automatically and thus should not be held liable as per "innocent owner" defense but both lower courts rejected this argument leading to appeal in Supreme Court where majority upheld these rulings stating ignorance doesn't absolve one from statutory obligations.

In the dissenting opinion for Harold E. Staples, III v. United States (1993), Justice Thomas argued that the majority's decision to uphold Staples' conviction was inconsistent with both legal precedent and common sense understanding of criminal law principles. He contended that it is a fundamental principle in American jurisprudence that an individual must have knowledge of his wrongdoing to be held criminally liable, especially when severe penalties are involved as they were in this case. In other words, he believed there should be proof beyond reasonable doubt that Staples knew his weapon had automatic firing capabilities before he could be convicted under the National Firearms Act (NFA). Furthermore, Justice Thomas criticized the majority for failing to consider how their ruling might impact innocent gun owners who unknowingly possess firearms regulated by NFA but lack any intent or awareness of violating federal laws.