Murder is the intentional, premeditated killing of another human being. The premeditation requirement for murder was historically described in the law as “malice aforethought.”

Laws regarding murder vary from state to state, and some states have a separate criminal offense of capital murder, which usually involves the most egregious circumstances, such as killing a peace officer in the line of duty or lying in wait to ambush and kill the victim. Capital murder offenses carry a potential death penalty.

And some states use the distinction of first degree murder (done with premeditation and punishable by death or life in prison) and second degree murder (generally an intentional killing without premeditation—also known as manslaughter or voluntary manslaughter in some states).

The criminal offense of murder is generally located in a state’s statutes—often in the penal or criminal code.

In Wisconsin, murder is classified under the terms 'first-degree intentional homicide' and 'second-degree intentional homicide.' First-degree intentional homicide, as defined in Wisconsin Statutes section 940.01, is the intentional and premeditated killing of another person with 'malice aforethought.' This is the most serious homicide offense in Wisconsin and carries a mandatory life sentence. There is no death penalty in Wisconsin, as it was abolished in 1853. Second-degree intentional homicide, covered under section 940.05, involves intentional killing without premeditation. This offense is generally considered when there are mitigating circumstances that make the crime less severe than first-degree intentional homicide. The distinction between first and second-degree intentional homicide in Wisconsin reflects the historical concept of 'malice aforethought' and the level of premeditation involved in the crime.