TWIN TROUBLE

Australian 29-year-old twin sisters were practising with small-calibre guns at the Family Shooting Centre outdoor shooting range south of Denver, Colorado, when they suddenly fell to the ground almost simultaneously from gunshots to the head.

Police Captain Perea said investigators are not sure who fired the gun or guns or whether the same bullet hit both sisters, who were in the same shooting lane.
One of the Victorian women died at the scene, the other was seriously wounded.

"Apparently the ladies were shot simultaneously or thereabouts," Mr Hamilton said."The how and the why, we really don't know."
Surveillance cameras show the women falling backwards out of their shooting stall.

NEURO LAW

Natural Born Killer

Dysfunction in a gene called MAOA, the so-called "warrior gene," can help express psychopathic behaviour.

The version of the gene that a person carries may determine or at least significantly influence whether a traumatic childhood experience of violence leads to psychopathy.   Wikipedia 

The gene inhibits serotonin reception in the impulse-control region of the brain.

Combined with exposure to abuse or trauma, studies show that the defect makes people highly susceptible to violent crime.

Because the MAOA gene gets passed down only on the X sex chromosome of mothers, more men than women are psychopaths.
For a man, only one X chromosome is inherited - the one from his mother, so, lacking an alternative, it gets expressed. A woman on the other hand gets an X from each parent, so that the normal MAOA gene usually inherited from her father can overrule a warrior one from her mother.