<human>:  When is a serial killer considered to be a serial killer?
<bot>: A serial killer is someone who kills three or more people, in separate events, over a period of time. Serial killers are often characterized by a pattern of behavior, such as a specific type of weapon or method of killing, or a specific type of victim. Serial killers are often motivated by a desire for power, control, or sexual gratification. Serial killers are often very intelligent and capable of planning and carrying out their crimes. Serial killers are often very dangerous and unpredictable, and should be considered extremely dangerous.