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 New Hampshire, the felony murder rule is codified under RSA 630:1-b of the New Hampshire Criminal Code. This rule stipulates that a person is guilty of murder if they commit or attempt to commit a felony that is punishable by life imprisonment, such as arson, robbery, burglary, kidnapping, or any Class A felony, and in the course of and in furtherance of such crime they cause the death of a person other than one of the participants. This means that if a death occurs during the commission of a qualifying felony, all participants in the felony can be held liable for murder, regardless of who actually caused the death. This includes accomplices such as lookouts or getaway drivers. The rule applies even if there was no intention to kill, 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 to note that the specific application of the felony murder rule can vary based on the circumstances of the case and the interpretation of the law by the courts.