Felony Murder, which is different than homicide, mitigated homicide or negligent homicide in that you can be held accountable for a homicide that someone else causes if its in the course of a commission of a felony offense by you and one or more other individuals. The simple example is if you are the getaway driver during a bank robbery and someone is killed while the others are robbing the bank. It doesn’t matter if you were in fact planning on killing anyone or if you wouldn’t have been involved if you had known. (Montana is different that perhaps every other state in the union in that it doesn’t have to be a separate felony from the one that kills the person for it to be felony murder, but it isn’t the first time Montana has taken the pragmatic route instead of the principles that other state’s follow.
An interesting article on its application and the extent it can be used is here.