What exactly is the felony-murder law?

In essence, felony murder means that all persons engaged in a felony are liable for murder if one of them kills a person during the crime. The precise definition and elements of "felony-murder" vary from state to state, but generally, it is a principle of criminal liability which holds someone legally liable for murder if, during the course of committing a serious felony with another person, the death of someone other than one of the participants in the crime is caused. A "serious felony" is one like arson, robbery, burglary, kidnapping, or rape. Most states also apply the felony-murder rule to situations where the death occurs during the immediate flight from the crime. It can also be applied if the perpetrators didn't complete the underlying crime and thus only attempted to commit the crime, if someone dies during the attempt. Some states provide that it is a defense to felony murder if the defendant was unarmed and had no reason to believe that any of his confederates was either armed or intended to engage in any conduct dangerous to life. An example: Two people rob a bank, one sits outside in the getaway car. The actual robber ends up shooting and killing someone in the bank during the robbery or while running away. The driver of the getaway car is liable for murder under the felony-murder rule, even though he had no knowledge his accomplice was going to kill someone and even though he didn't participate in the killing, if he knew his accomplice had a gun which he was intending to flash inside the bank when demanding the money.