In the United States, most states categorize murder by degree, as originally defined by the Pennsylvania Method of classification. Although laws vary by state, the basics are the same. In general, murder is a crime committed with malice aforethought, meaning that the killer intended to kill or at least seriously harm his victim. The distinction between the degrees of murder can be blurred, and each case is usually considered according to its own circumstances.
First-degree murder is the most serious class of murder. The defendant kills with premeditation, deliberation and some element of malice. In practical terms, a prosecuting attorney must prove that the defendant planned to kill his victim and was aware that his actions would result in the victim's death. In some states certain types of murder are automatically classified as first-degree. Examples would be killing by poison or bomb. In addition, most states have laws specifying that a defendant who kills his victim while committing a felony must be charged with first-degree murder. In some jurisdictions, criminals who commit first-degree murder face the death penalty.
Second-degree murder is killing without premeditation or deliberation. It's clear that the defendant intended to harm the victim, but not that he intended to kill him. Second-degree murder charges often arise after a defendant intended to assault a victim, but ended up killing him. The sentence for second-degree murder varies according to the state where the crime was committed, but generally involves a period of imprisonment. In serious cases, a court may sentence a criminal to life imprisonment.
Third-degree murder is sometimes referred to as manslaughter and can be defined as a killing that does not involve malice aforethought. The crime does not exist in all states. Third-degree murder is sometimes further classified by being either voluntary or involuntary. Voluntary manslaughter may arise, for example, if an individual is suddenly provoked and commits the crime while in the heat of anger or passion. In involuntary manslaughter, the defendant is guilty of recklessly disregarding the risks involved with his actions, resulting in the death of his victim. The distinction between second- and third-degree murder is not always clear.