Not to pick nits, but, well, to be nitpicky about it - both serial and spree killers are mass murderers. Those are two of the subtypes of mass killings. Also, I don't think Jason would really fit as a spree killer, though I'm not sure what classification would really fit, heh.
I think I learned that from Darin Morgan in a teleplay. Made sense to me so I just go with it. He said something along the lines of ...let me look it up.
Frank unwraps the gift. It's two videotapes; they are blood-and-guts horror flicks. Frank loses a portion of his holiday cheer.
FRANK (reading): "Black Christmas" and "Silent Night, Deadly Night". Whatever happened to "Miracle on 34th Street"?
ROEDECKER: Well, it ain't your father's Christmas! Nothing will put you more in the mood for Christmas than a serial-killing Santa!
FRANK: This is not a serial killer: he is a spree killer.
ROEDECKER (factually): The sexual repression and signature make him an organized serial killer.
FRANK (gesturing at the tape): The triggering stressor would be that they forced him to wear that Santa Claus outfit -- it's ludicrous.
ROEDECKER (beat): It says "Serial Killer" on the box.