Serial killers tend to be white, heterosexual, males in their twenties and thirties who are loners with low self-esteem. Their methodical rampages are almost always sexually motivated. Their killings are usually part of an elaborate sexual fantasy that builds to a climax at the moment of their murderous outburst. Serial killers generally murder strangers with cooling off periods between each crime. Many enjoy cannibalism, necrophilia and keep trophy-like body parts as mementos of their work. Serial killers are sadistic in nature.