Serial killers

Three murders with certain characteristics would normally indicate a serial killer.
Such murders are usually confined to one geographical area.

Mass murderers are terrorists.
Either that or immature adolescents who go to school and shoot everyone in sight, who are then either shot dead by the police or commit suicide.
They have a preference for guns and bombs that will cause the maximum amount of damage in a short space of time.
MMs don't care about the consequences of their actions because they know how it will end.

The concept of the MM is easier to grasp because he's "mentally unbalanced" and therefore easily distinguished from the rest of "us".

The serial killer, on the other hand, touches on something far more sensitive and complicated. The destructive instinct we all carry within us.

A serial killer doesn't just threaten our physical safety. He threatens our sanity. Because, whether we admit it or not, we all carry around in us a great destructive power. And have all, at some time, wondered what it would be like to give free rein to that desire to take someone else's life.

There are many reasons for this.
To put the world to rights.
To get revenge for something that happened in your childhood.
To vent your hatred of society.

SKs are neither perverted or sadistic. They are terrifyingly normal.
This normality is more terrifying than all their atrocities put together.

Some SKs have human motives.

Some are trying to put society to rights. Which is why they kill prostitutes.

SKs don't benefit financially or sexually from their crimes. They don't rape the victims or take their money.

Jack The Ripper and The Zodiac Killer were people trying to restore moral order and decency in their areas. They were never caught or ever identified.

SKs are usually only active for a sort period of time and then disappear completely, having left their mark on history.

SKs are hard to track because of the lack of motive.

Some leave a signature.
Some choose a type of victim - homosexual, prostitute, beggar.

Some are "asymmetrical killers" - they kill because they can't control the impulse to kill. When they reach a point where the urge is satisfied they stop killing. They start again when the impulse becomes unbearable.

Manson was trying to cleanse the world.
Ridgeway was trying to purify his home town.
Dahmer was trying to satisfy the appetite of the gods.

Most criminals don't want to be caught.
But they do want to be identified.

Some want to hit the headlines and gain fame and glory, like Jack The Ripper or Zodiac.

Others keep a diary so their grandchildren will be proud of them when they find it hidden in the attic years later.

Other have a message to deliver. Drive prostitutes away by making them afraid to walk the streets. When these SKs stop their murders it's because they believe their message has been received.