http://boingboing.net/2013/01/15/a-more-resilient-species.html

One of Brown’s studies covered the life and death of Charles Whitman, a college campus mass murderer, who, in 1966, on the University of Texas campus, killed 15 people and wounded another 31, after killing his wife and mother the previous evening.

Extensive interviews with those who knew Whitmore, revealed that a “lifelong lack of play” had been an important factor in his psychopathology. Whitmore was always pressured by his parents to “do something useful” -- the antithesis of self-directed play. 

In the course of his research and through extensive interviewing, Brown found that many violent criminals shared this same lack of childhood play.