First degree murder is either a homicide committed 1) willfully and with premeditation and deliberation or 2) in the commission, or attempted commission, of an inherently dangerous felony.
Premeditation is simply deciding to kill before committing an act that causes death. Deliberation is when a defendant weighs the choices for or against killing and still decides to kill. There is no set amount of time needed to establish premeditation or deliberation; it can be established circumstantially and can be established even if a defendant had only an instant to make the decision to kill. Any decision to kill made impulsively or without consideration is not sufficient to establish deliberation for first degree murder.
A homicide is also considered first degree murder if it happens during the commission of an inherently dangerous felony. This is known as the felony murder rule. It is used as a substitution of the intent needed to prove regular first degree murder in that it uses the commission of the felony to establish the mental state of premeditation and deliberation, regardless of whether a defendant actually intended anyone to die. In other words, even if someone died accidentally during the commission of a specific enumerated felony, the defendant can still be charged and liable for first degree murder.
In order to find a defendant guilty of felony murder there has to be 1) an act causing death during an ongoing felony or an attempted felony, 2) the act causing death was a foreseeable consequence of the felony, 3) and the underlying felony was an inherently dangerous felony. Any participant in the commission of the underlying felony becomes liable for the act causing death and is subject to murder prosecution.
The act causing death has to be a foreseeable consequence of the felony. This element is most commonly satisfied by committing an enumerated felony that the legislature has deemed always dangerous to commit, or by defendants using a deadly weapon; use of a deadly weapon during a felony usually makes the killing foreseeable. The most common enumerated inherently dangerous felonies are mayhem, rape, sodomy, burglary, arson, kidnapping, escape and robbery. For example, if a person uses a gun to commit a robbery, a common enumerated felony, even if never intending to fire it; if the gun goes off at any point during the robbery, whether intentionally or unintentionally, the felony murder rule would then apply and a defendant, as well as any co-participants in the felony, could be charged with first degree murder.
In order to qualify as felony murder, the act causing death has to occur while the felony is ongoing. The timeframe that meets this requirement stretches from the time when the felony was attempted until the defendants reach a place of temporary safety. If the act occurs between these two points in time, then the ongoing requirement is satisfied. The victim need not die during the commission of the felony, but the act which causes death must occur during this time frame.
As to any murder, generally states will set specific time periods a victim needs to die in, such as one year and one day, subsequent to the act causing death for the defendant to still be charged with murder. Statutes of limitation on murder do not exist and therefore it becomes important if a defendant is not caught for a long period of time after commission of the act, or if a case is pending for a long period of time while a defendant is waiting resolution of his/her case, and a victim is in critical condition. If the case is to resolve before a victim dies, the most a defendant can be charged with is an attempt. If a victim were to die while a case was still open, the prosecution can, and generally does, amend complaints and indictments to charge murder.