(Andres Leighton | AP file photo) A Virgin Mary painting, flags and flowers adorn a makeshift memorial for the victims of the mass shooting at a Walmart in El Paso, Texas, Aug. 4, 2019. The vast majority of mass shooters have acquired their firearms legally with nothing in their background that would have prohibited them from possessing a gun. But there have been examples of lapses in the background check system that allowed guns to end up in the wrong hands.