Connecticut killer: Lonely, but intelligent young man

Adam Lanza, of the Connecticut school massacre was a loner and intelligent. What makes these youngsters turn to blood thirsty monsters?

Adam Lanza was such a loner that even 24 hours after the massacre, no one came forward with a claim of fleeting friendship with this loner.
Neighbours are of the opinion that parents' divorce hit hard on the kid.
What an irresponsible parenting!