WASHINGTON -- Gun control advocates acknowledge that the expanded background checks they want would not have prevented the Las Vegas massacre. But last week, they went to court to try to make Nevada enforce the background checks that are already on the books.

Last year, the NRA spent more on a Nevada ballot initiative than in any congressional race, fighting a proposal to expand background checks, including at gun shows. Gun control advocates spent twice as much and won a narrow victory.

Nearly a year later, however, the law is not being enforced. State and federal officials are in a standoff over who does the background checks on private gun transfers.

So at a Reno, Nevada, gun show just days after the country's deadliest mass shooting in Las Vegas, video released by Everytown for Gun Safety shows a private investigator licensed in Nevada easily and legally buy four semi-automatic rifles and a 100-round capacity magazine without any background checks.

Nevada Attorney General Adam Laxalt, who campaigned against the measure for the NRA, initially argued it isn't enforceable because the law explicitly says the FBI has to conduct the background checks, not the state. He cited a letter from the FBI that says Nevada law "cannot dictate how federal resources are applied."

John Feinblatt CBS News

But John Feinblatt, the president of Everytown, says Laxalt and Nevada's Republican Gov. Brian Sandoval should negotiate a solution that uses federal and state background check systems.

"If they need to get on the phone with the FBI and work it out, they should do that today," he said. "The governor and the attorney general are turning this into a political football."

Three days after the Las Vegas shooting, Sandoval asked Laxalt to reexamine this question. Laxalt returned with an opinion last week saying Sandoval has the authority to go back to the FBI with a "proposed policy solution," furthering what appears to be a game of hot potato when it comes to the state's gun laws that is now going to be fought in the courts.