In psychology, there are three major personality traits in children that are said to be warning signs for the tendency to become a serial killer. They were first described by JM MacDonald in his article The Threat to Kill in the American Journal of Psychiatry , pages 125-130 in 1963.

• Firestarting, invariably just for the thrill of destroying things.
• Cruelty to animals. Most children can be cruel to animals, such as pulling the legs off of spiders, but future serial killers often kill larger animals, like dogs and cats, and frequently for their solitary enjoyment rather than to impress peers.
• Bedwetting beyond the age when children normally grow out of such behaviour.