Gun reform advocate Sen. Chris Murphy (D-CT) is pushing to reintroduce a bill to require mandatory background checks on every commercial gun sale or transfer after yet another mass shooting this week. The bill would include requiring background checks on online sales and gun show sales. New York and Connecticut “crime guns” are often bought in states that don’t have universal background checks, Murphy said on CNN This Morning Thursday. “If you want to buy a gun, you just should have to prove that you’re not a criminal, that you’re not seriously mentally ill,” he said. “The problem is, many states have chosen not to apply background checks to internet sales and sales at gun shows. That means the criminals know how to buy guns without being detected as a criminal.” Three students were killed, and five more injured, in a shooting at Michigan State University on Monday night. The gunman, who later killed himself, had two legally owned handguns that were unregistered.