Opponents of expanded gun background checks argue that they would not prevent criminals from acquiring guns because many get them through back-market sales or theft, or by getting “straw purchasers” – people who can pass background checks – to buy guns on their behalf, says the New York Times. The checks blocked purchases. Since 1998 more than a million potential sales have been rejected – usually because the would-be buyers are convicted felons or fugitives from justice, or they have been involuntarily committed to a mental health institution. When the FBI cannot immediately determine whether would-be buyers have criminal or psychological records that would bar them from owning guns, it is given 72 hours to clear it up. If it fails to complete the background check by then, the buyer is allowed to return and purchase the gun. Roughly 3,000 firearms were sold to prohibited buyers through this loophole last year. Dr. Garen Wintemute, director of the Violence Prevention Research Program at the University of California, Davis, said his research indicated that denying firearms to prohibited people reduced their likelihood of being subsequently arrested for gun crimes between 25 and 30 percent. “I think we have good evidence that background checks work,” he said.