With that and some other odd aspects of his behavior which Johnson claimed was out of character (eg starting an alterction and stealing in the store), I wonder if he was suffering from Toxoplasmosis or some similar condition. Toxoplasmosis is thought to dramatically affect an individual's appetite for risky behavior. Preliminary research suggests that as you'd expect there 's a higher seroprevalance in prison populations, but much more work needs to be done to verify this.

http://en.wikipedia.org/wiki/Toxoplasmosis