Since the elemntary school shooting massacre in Newtown, Connecticut in  December, politicians and policymakers have been debating how to make gun policies -- and society at large -- safer. Part of the answer might lie in understanding the science of what compels a person to open fire upon innocent people. In a new documentary produced by NOVA, journalist Miles O'Brien investigates how far neuroscientists have come in determining what makes the brain of a violent  adolescent  different than that of a normal brain.   Perhaps most importantly, he asks whether that science can help to identify potential shooters earlier and prevent future tragedies. His report, "Mind of a Rampage Killer," is part of PBS's "After Newtown" initiative, a series of documentaries, news reports and public affairs programs.   The NOVA program airs on PBS stations at 9pm/8c on Wednesday night; see a short excerpt here.