I believe I read in Florida that non US citizen are not allowed to purchase a firearm unless they have a hunting license ( he apparently did have a valid hunting license ) so the background check worked as it was supposed to . He would have also had military clearance so unless something else comes up we haven’t seen yet , he was legally able to purchase the firearm and would have passed any background check . We can pass as many laws as we want to pass and tweak them every day , but we will never be able to legislate the evil in a persons heart . That’s just a cold hard fact .