Staples v. United States, 511 U.S. 600 (1994) involved a semi-automatic rifle, for which registration under the Act is not normally required. The rifle, however, had been modified for fully automatic fire, a modification which did trigger the registration requirement of the Act. Id. at 603. Because the modification was accomplished without visible, external signs of tampering and the defendant maintained that he was unaware that the rifle had been so modified, the Court held that the government is required to prove that a defendant knows of the features of the weapon that bring it within the scope of the Act. Id. at 619. The defendant was charged under the National Firearms Act (26 U.S.C. 5801-5872), which imposes strict registration requirements on all statutorily defined "firearms." The statute defines "firearm" to include a machine gun which is defined as any fully automatic weapon. (26 U.S.C. 5845(a)(6), (b).) The defendant was found in possession of an unregistered AR-15, which is a semi-automatic weapon unless modified. Expert testimony established that the weapon in the defendant's possession had been modified to operate as a fully automatic weapon, although the defendant testified that while the gun was in his possession, it had only operated semi-automatically. Finding the statutory language silent on the requisite mens rea, the United States Supreme Court concluded that silence on this point "did not necessarily suggest that Congress intended to dispense with a conventional mens rea element, which . . . require[s] that the defendant know the facts that make his conduct illegal." (Staples, supra, at p. 605.) The court rejected the government's claim the statute created a strict liability regulatory offense which restricted the circulation of dangerous weapons. ( Id. at pp. 606, 616.) The court reasoned in part, that dispensing with mens rea under the statute would criminalize apparently innocent conduct by applying to guns that fell outside the statutory definition of firearms, and which "traditionally have been widely accepted as lawful possessions . . . ." ( Id. at p. 612 [at p. 620].) The Court held that even in cases involving strict liability, "the defendant must know that he is engaged in the type of dangerous conduct that is likely to be regulated" and that "a knowledge requirement" has been read into "public welfare crimes." Staples bears no similarity to the present case and certainly would not be expected to alert trial counsel to a potential constitutional argument under R.C. 2907.02(A)(1). Staples addressed whether a statute criminalizing the possession of an unregistered machinegun required proof that the defendant knew the weapon "had the characteristics that brought it within the statutory definition of a machinegun." Id. at 602. The Supreme Court concluded, as a matter of statutory interpretation, that it included a mens rea requirement. The Court's opinion said nothing about whether the lack of such a requirement would violate due process. In fact, the majority noted that Congress "remains free to amend the statute by explicitly eliminating a mens rea requirement." Id. at 615 n.11. In Staples, the Court considered the mens rea requirement of the National Firearms Act, 26 U.S.C. 5861 (d) (1994) ("Act"). The Court held that in order to be convicted under the Act of possession of an unregistered firearm, the government must prove that the accused knew the weapon that he or she possessed had the physical characteristics that brought it within the scope of the Act. Staples, 511 U.S. at 619.