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 Montana, the felony murder rule is codified in the Montana Code Annotated (MCA). According to Montana law, a person commits the offense of deliberate homicide if they purposely or knowingly cause the death of another human being. The felony murder rule applies when a death occurs during the commission or attempted commission of a forcible felony, such as robbery, sexual assault, arson, burglary, kidnapping, or any felony involving the use or threat of physical force or violence against an individual. Under this rule, all participants in the felony can be held criminally responsible for any deaths that occur during or as a result of the felony, regardless of their direct involvement in the death. This means that accomplices such as lookouts or getaway drivers can be charged with deliberate homicide even if they did not personally cause the death. The intent to kill is not a necessary element for felony murder charges under Montana law; the mere participation in the underlying felony that leads to a death is sufficient to establish liability for deliberate homicide.