Psychology Dilemma

‘Dark patch’ visible in brain scans of killers and rapists, neurologist claims

Can you spot evil in an X-ray?You can, at least according to a German scientist who claims an "evil patch" is visible in brain scans of criminals.
Dr. Gerhard Roth, a neurologist and professor at the University of Bremen, told London's Daily Mail that he discovered a dark mass near the front of the brain in scans of people with criminal records.
"When you look at the brain scans of hardened criminals, there are almost always severe shortcomings in the lower forehead part of the brain," Roth said. "There are cases where someone becomes criminal as a result of a tumor or an injury in that area, and after an operation to remove the tumor, that person was completely normal again."
He added, "This is definitely the region of the brain where evil is formed and where it lurks."
Roth is not alone in his belief that brain scans can reveal psychopathic tendencies.
Kent Kiehl, associate professor of psychology at the University of New Mexico, for one, used a mobile MRI unit to conduct brain scans on 2,000 prison inmates in Wisconsin and New Mexico.
Kiehl found similar patterns in their brain scans. “If you have different behavior, you’re going to have a different brain," he said at a 2012 lecture at Duke University:

Kiehl noted the role of the MAOA gene in violent behavior. He said if one has the gene and comes from a stressful environment, he or she has a significantly elevated risk for committing a violent offense. The gene may contribute to variability in grey matter density in some parts of the brain, which is a risk factor for psychopathy.

“Psychopathy is currently considered the single best predictor of future behavior,” Kiehl said.
Roth agrees: "When I will look at young people, and I see there are developmental disorders in the lower forehead brain, I can say that there is a felon in the making with 66 percent probability."
A growing number of psychologists "believe that psychopathy, like autism, is a distinct neurological condition—one that can be identified in children as young as 5," the New York Times reported in May. "Crucial to this diagnosis are callous-unemotional traits, which most researchers now believe distinguish 'fledgling psychopaths.'"
Not all psychologists believe such a diagnosis is possible, and even those that do admit they are uncomfortable with it.
"No one is comfortable labeling a 5-year-old a psychopath.” Mark Dadds, a psychologist at the University of New South Wales, told the Times. "[But] the research showing that this temperament exists and can be identified in young children is quite strong.”
Roth himself admits the research is not foolproof.
"Of course it is not automatic," he told the Daily Mail. "The brain can compensate somewhat for violent tendencies, and it is unclear how that works."

I'm not sure if there's really a 'dark patch' in the brain but psychology always believe in the nature and nurture theory. So in the event when there is really a biological reason for a certain behavior, does it mean that the person is not to be blame. For instance, if there's a murderer or rapist gene/disorder, does it mean that engaging in murder or rape is beyond their control and hence should be dealt with leniently? Or in another way, if it's biological/nature and cannot be changed, should they be killed so it do not have the chance to do it again? 

By the way, another question which is linked to this. 
For the serial rapist/murders/paedophiles...
Are they BAD or are they MAD?