"Criminal justice reform has played a major role in the congressional agenda over the past several Congresses, with sentencing reform bills making up the majority of the legislative action on this issue. However, some reformers have also highlighted the need to strengthen the 'mens rea' requirements in federal law. 'Mens rea', Latin for 'guilty mind,' is the mental state the government must prove to secure a conviction. For instance, some laws require that the prosecution demonstrate that the defendant 'intentionally' have committed the act in question--that is, committing the act with the conscious desire for the harmful conduct to occur--while others require that the act be done 'knowingly' or with 'reckless disregard' of the harm it may pose. Some modern statutes require no 'mens rea' at all; these are commonly referred to as strict liability offenses. Unlike the Model Penal Code, which includes four categories of 'culpability' or moral blameworthiness, the Federal Criminal Code, found largely in Title 18, does not create uniform mens rea standards. Instead, each statute may or may not contain a mens rea element depending on the statute. Supplementing the statutory text, the Supreme Court has developed a set of presumptions to apply when a mens rea term is omitted. However, the Court has applied these rules in a somewhat ad hoc fashion depending on a variety of factors, including the origin of the offense in question (e.g., common law or statutory); the severity of the penalty imposed; and the purpose behind the law (e.g., penal or regulatory)."
CRS Report for Congress, R44464
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html