Mens Rea
Definition
Mens rea ("guilty mind") refers to the mental state required for criminal liability. The Model Penal Code identifies four levels of culpability in descending order of blameworthiness: purposely (conscious objective to engage in the conduct or cause the result), knowingly (awareness that conduct is of a certain nature or practically certain to cause the result), recklessly (conscious disregard of a substantial and unjustifiable risk), and negligently (failure to perceive a substantial and unjustifiable risk). The required mens rea varies by offense and must be proven beyond a reasonable doubt.
Example
A defendant fires a gun into a crowd. If the defendant's purpose was to kill, this satisfies the highest mens rea. If the defendant knew death was practically certain, this is knowledge.