US mass shooters exploited gaps, errors in background checks

Most mass shooters in the U.S. acquired the weapons they used legally because there was nothing in their backgrounds to disqualify them, according to James Alan Fox, a criminologist with Northeastern University who has studied mass shootings for decades. Not all gun purchases are subject to a federal background check system. In 2018, there were more than 26 million background checks conducted and fewer than 100,000 people failed.