There are no degrees of murder at common law. It is a modern statutory rule which divides murder into degrees according to its mens rea, but the exact definition of second-degree murder varies by jurisdiction.
Both first-degree murder and second-degree murder are intentional homicide crimes. First-degree murder is the most serious charge - a deliberated and premeditated murder. Deliberation and premeditation are the main elements that distinguish it from second-degree murder, reflecting the defendant’s intention to plan for killing someone. The premeditation time should be adequate after the intent of killing occurs (e.g., immediate killing without a plan cannot be defined as first-degree murder, unless it’s a felony murder). First-degree murder can only be established by statutes. For instance, in some jurisdictions, felony murder is defined as first-degree murder by statutes. If there are no statutes about it, then it is classified as second-degree murder. Felony murder is a homicide committed when the defendant prepares an inherently dangerous felony regulated by statutes, like burglary, rape, robbery, arson, or kidnapping.
Second-degree murder is typically murder with malicious intent but not premeditated. The mens rea of the defendant is intent to kill, intent to inflict serious bodily harm, or act with an abandoned heart (e.g., reckless conduct lacking concern for human life or having a high risk of death). Excepting felony murders triggering first-degree murder, other murders, which occur when felonies are committed, usually are second-degree murders. The punishment for second-degree murder is less severe than that for first-degree murder. Capital punishment is not available for a second-degree murder conviction.
Lack of mens rea can be a defense to reduce murder to manslaughter. According to the mens rea, first-degree murder is a specific intent crime, while second-degree murder is a malice crime, which makes their mens rea negated differently. For example, voluntary intoxication can be a defense of a specific intent crime to prevent the formation of its required intent. Thus, it prevents the formation of the premeditation of first-degree murder, but not second-degree murder. Killing a victim in a drunken rage is second-degree murder, as voluntary intoxication cannot reduce malice crime of murder down to manslaughter.
[Last updated in May of 2022 by the Wex Definitions Team]