Hi David.

I've been asked a couple of times for a definition.

I gave this one to Bruce McGraw this morning:

My working definition is actions where the motivation of the perpetrator is the gratuitous pleasure in the suffering or death of others. One example might therefore be a serial killer. These are only song lyrics, but I think the Doors got it exactly right in Riders on the Storm:

“ There's a killer on the road. His brain is squirmin' like a toad. Take a long holiday. Let your children play. If you give this man a ride, sweet family will die. Killer on the road, yeah”.

I'll have a look at the rest of this later.