The difference between capital murder and first degree murder is minimal; capital murder is first degree murder if the state allows the death penalty. First degree murder is a type of murder that is both intentional and premeditated, such as when the perpetrator plans to kill the victim and succeeds. Capital murder is any first degree murder that can be punished by death penalty in the states that practice capital punishment.
TL;DR (Too Long; Didn't Read)
First degree murder may be charged in most states when the perpetrator committed the crime with the intent to kill the other person; in some states, felony murder is considered first degree murder. Capital murder is simply first degree murder that is punishable by death in that particular state.
Murder Must Be Intentional and Premeditated
While states may have slightly different definitions, first degree murder has to be premeditated, which means the criminal thought about the crime ahead of time. It is also deliberate, meaning that the criminal carried out the crime in full awareness of what he or she was doing. Some states include the phrase "with malice aforethought" which means the same as intentional – the deliberate, planned taking of a person's life. First degree murder may be committed by hand or with the use of a weapon, explosive, a weapon of mass destruction, armor-penetrating ammunition, poison or torture.
The Felony Murder Rule
Some states also have a felony murder rule, which provides that if a person dies during the commission of a dangerous felony, such as armed robbery, the perpetrator may be charged with murder in the first, even if the intent was not to kill. Felony murder is first degree murder and is a capital offense, although the death penalty cannot be imposed upon a defendant who played only a minor role in the underlying felony.
Capital Murder is First Degree Murder Punishable by Death
Capital murder is a type of first-degree murder for which the death penalty is authorized by law. California, Texas and other states with capital punishment usually authorize execution for first degree murder that is aggravated by special circumstances, for instance the murder of a police officer or firefighter while that person was on duty.
Capital Murder Versus First Degree Murder
First degree murder always has the potential to be classified as a capital murder in states that allow the death penalty, even if the perpetrator ultimately is not sentenced to death. Certain types of murders may be elevated to first degree murder and thus capital murder, such as paying someone to commit a murder, murdering someone while escaping prison, murdering a child and murder while hijacking an aircraft are also potentially special circumstances that would elevate the crime to capital murder.
The Difference Between Life and Death
Punishment for first degree murder is severe, requiring a lengthy time in prison, up to the extreme of a life sentence. The purpose of the sentence is as much to protect the public from a dangerous person as it is to punish the murderer. The punishment for those convicted of a capital murder is capital punishment, or the death penalty, which is currently recognized by 31 U.S. states. The difference in the crimes may be subtle, but it is literally the difference between "life" and "death."