This criminal psychologist explains in one sentence why murderers aren't evil

But Loyola University psychologist James Garbarino, who has spent decades studying the minds of killers, offers a different reading of their violent behavior.

In a recent talk at Cornell University, he boiled it down to a single sentence: 

"Most of these killers are best understood as untreated, traumatized children who inhabit and control the minds, hearts, and bodies of adult men."

Garbarino was speaking in support of his new book "Listening to Killers: Lessons Learned from My Twenty Years as a Psychological Expert Witness in Murder Cases." 

He explained the traumas of childhood are simply too much for most young brains to handle. By the time people reach their teenage years, a life of violence, poor education, and drugs - both in and out of the home - make for a devastating psychology. 

"A jury looks at them in the chair and thinks, 'What a stone-cold killer this is,' when in fact what they're looking at is an untreated, traumatized child whose dissociation is how he survived," he says. "And now it comes back to haunt him."

Garbarino represents a more sympathetic approach to criminal justice - one that's starting to gain footing in the US. 

Last month, Chicago's Cook County Jail, the second-largest in the country, announced it was hiring psychologist Nneka Jones Tapia as its new executive director. An estimated one-third of the jail's inmates suffer from mental illness. 

You can watch Garbarino's entire talk below: