The felony murder rule is a legal doctrine that expands the definition of murder and makes criminal accomplices (including a lookout or getaway driver) as responsible for a death that occurs in the course of a dangerous felony crime as the person who directly caused the death by pulling the trigger of a gun, stabbing the victim with a knife, strangling the victim, or otherwise causing the victim’s death. Examples of dangerous felony crimes that implicate the felony murder rule include robbery, burglary, rape, aggravated kidnapping, carjacking, and arson.

When the felony murder rule applies, it may make a criminal accomplice liable for murder even if the criminals had agreed that no one would be killed in the course of the crime, and even if it is a fellow criminal who is killed in the course of the crime—such as when a police officer or security guard shoots a bank robber—which may result in all other accomplices to the crime being charged with murder.

In many states the felony murder rule—and any distinctions between the culpability of accomplices and principals to a crime—are located in the state’s statutes—often in the penal or criminal code.

In Idaho, the felony murder rule is codified in the state's statutes under Idaho Code § 18-4003(d). This rule stipulates that a killing, whether intentional or not, that occurs during the commission of or an attempt to commit arson, rape, robbery, burglary, kidnapping, or mayhem, or while resisting or attempting to escape from lawful custody, is considered murder of the first degree. This means that if a death occurs during the commission of one of these felonies, all participants in the felony can be held criminally responsible for murder, regardless of their direct involvement in the death. This includes individuals who may have served as lookouts or getaway drivers. The rule applies even if the death was accidental or unintended, and it can also apply if a co-felon is killed, for example, by law enforcement during the commission of the crime. It's important for individuals to understand that participation in a felony that leads to a death can result in severe legal consequences under the felony murder rule in Idaho.