How not to pose

Couldn't help but notice the goofy grin on the face of Thomas Caffall, the Texas A&M shooter, when his picture was released last night:

It reminded me of the look I'd seen on two other faces in the news. Most recently, of James Holmes, the Aurora, Colorado movie theater shooter:

And before that, of Jared Loughner, the January, 2011 Tucson shooter:

The only picture that would have alarmed me on its own was the bottom one, of Jared Loughner, but his unhinged look stems from his blackened left eye and shaven head. Hold your hand over the top of Loughner's face and his smile appears the same as the other two.

Their expressions seem to be halfway between foolish grins ("Okay, so I'm a pervert, so what?") and smirks ("I'm going to kill a whole lot of people and you have no idea").

Is this the new look of mental illness?