Somebody Has Murdered a Dark-Haired Pre-Pubescent Girl in the Area

Somebody has murdered a dark-haired pre-pubescent girl in the area last year and left her mutilated body near the train tracks. This year, another dark-haired girl of about the same age was murdered and her body left near the train tracks in the same general area. According to the textbook, can it be a serial killer's job?

A) Yes because there are enough similarities between the two cases.
B) Not conclusive because there were less than 3 cases with similarities.
C) Only if there is DNA evidence left on the scene of both crimes.
D) It is either a serial killer or a mass murderer.