The first definition of first degree murder is causing the death of another person with either the intent or knowledge that the conduct will cause death and with premeditation. Premeditation is often described as 'malice aforethought,' which basically means that you probably considered the consequence of your conduct for at least a second before you committed the act.

The second definition of first degree murder is causing the death of another person while committing or attempting to commit another crime like sexual conduct with a minor, sexual assault, molestation of a child, various drug-related crimes, kidnapping, burglary, arson, robbery, escape from jail, child abuse, or unlawful flight from a pursuing law enforcement vehicle, or while fleeing from the scene where you committed any of these offenses.

The third definition of first degree murder is causing the death of a law enforcement officer in the line of duty while intending or knowing that the conduct will cause the officer's death.

Any kind of first degree murder is a class 1 felony and is punishable by death or life imprisonment. In Arizona, the trial jury decides whether the defendant has committed first degree murder. Then the judge holds a separate sentencing hearing to determine the proper sentence. A.R.S. § 13-703 outlines the various 'aggravating' and 'mitigating' factors that the judge must consider in reaching a decision about whether to impose the death penalty.

Recently, the Arizona case State v. Ring went before the United States Supreme Court. The Court decided that Arizona's system of jury-conviction and judge sentencing (which is similar to the system in several other states) is un constitutional. This means that now a jury must find a person guilty of First degree murder, and also approve of the death sentence being given as punishment for the murder.