In its simplest definition, murder is the illegal killing of another with malice aforethought. It is the presence of malice that distinguishes murder from other forms of homicide, i.e. manslaughter. This is the most serious crime on the books, and those convicted of it may face a life sentence or possibly the death penalty. Generally speaking, there is no statute of limitations on murder.
There are four recognized states of mind that constitute malice, and they are the intention to kill, the intention to inflict grave bodily harm but not murder, the careless lack of concern to an action that is high risk to human life and/or the intention to commit a felony-murder.
In the U.S., if murder is committed within a state’s borders, the state has jurisdiction. If the crime involves a federal employee or was committed on federal property or crossed state lines, the federal government also has jurisdiction. If the murder is not committed in any state, then jurisdiction is exclusively federal. In cases where a murder involves the federal and state authorities, the murderer may be tried and punished twice and not face the doctrine of double jeopardy. There are 51 jurisdictions and each one has its own criminal code.