Serial killer - will never stop, not until he is, and he usually has a style of victim, a way of killing that’s personal and also is generally either a psychopath or a sociopath.
Spree - something kicked them off, and they’re running with it, usually kind of literally but with cars, and they also generally won’t stop until they’re made to and females are more common in spree than serial.
Mass - think killing on a grand scale, the Las Vegas shooter, school shootings, killing their entire family and I don’t mean just mum and dad. Something happened that made them snap in a way that all they want to do is kill as many as possible, can have illusions of grandeur where it seems to them this is what seems ‘fair’ or is justified retribution.
