Murder involves a specific intention and forethought to kill someone. It’s the worst type of homicide and its severe penalties reflect that – convicts can face life imprisonment without parole or even the death penalty, depending on jurisdiction. These harsh punishments help deter and punish murderers, and also reflect the value that society places on human life.

During legal proceedings, murder is classified according to a criminal law concept called mens rea, which refers to the state of mind of the offender. A greater intent to kill generally results in a higher charge and more severe consequences, such as first-degree murder versus second-degree or third-degree murder. However, a distinction between intent and premeditation (e.g. killing a loved one in the heat of passion or killing a bully in retaliation) is often a matter of interpretation, and jury sympathies can play an important role.

In addition to the presence of intent, prosecutors must demonstrate that the killer acted with malice aforethought in order to secure a conviction for first-degree murder. This is typically done by examining actions that indicate a deliberate plan (for example, preparing for the killing, taking the time to consider their options, or hiding evidence) as opposed to crimes of passion or the sudden decision to kill in the course of committing another felony such as burglary, rape or robbery.

The most common motives for murder include revenge, vengeance, jealousy, anger, and greed. Various biological factors can also impact motives for homicide, such as the reduction of serotonin during stress or testosterone in an individual who is under pressure to compete or win, or when a loved one has a disfiguring disease or condition.