OAK HARBOR, Wash. — Prosecutors in Island County have filed what is believed to be the first criminal charge for a violation of Washington’s 2014 gun background check law.

Mark Mercado, 25, was charged last week in Island County Superior Court with unlawful transfer of a firearm, KING-TV and Northwest News Network reported. Prosecutors say he sold a handgun to David Nunez in November 2015 which they believe was used the next night to murder 17-year-old John Skyler Johnson.

Washington voters approved Initiative 594 in 2014. It requires people transferring a firearm to go through a federally licensed firearms dealer to conduct a background check on the buyer. But prosecutors say Mercado sold Nunez the .22-caliber pistol without any such check.

“The focus of the law enforcement officers was they wanted to get the pedigree of the gun and find the gun so that it could be used in the murder prosecution,” said Island County Prosecutor Greg Banks. “But it occurred to us that, ‘Hey, this is also a gun that was transferred illegally and our job is to prosecute crimes when they are referred to us.’ And so we are.”

Nunez did not have a criminal record, but he was not allowed to buy a handgun because he was under 21 at the time.

Nunez has pleaded guilty in the murder along with three co-defendants and is serving a 25-year prison term.

Charging papers filed Friday say Mercado left his job and moved out of Oak Harbor after being questioned in the case. Authorities say they do not know where he is.

Initiative 594, sponsored by gun control backers, aimed to close the so-called “gun show loophole” and require a federal background check for private gun sales and transfers. Previously, only sales by gun dealers required a background check in Washington.

Opponents called the background check requirement an infringement on the rights of law-abiding gun owners and buyers. After the law passed, the Bellevue-based Second Amendment Foundation sued to try to block it, but a judge rejected the case.

Supporters of the law say it has stopped about 100 prohibited gun sales since taking effect.

According to charging documents, Nunez contacted Mercado via text message looking for a gun, and Mercado wrote back: “Not a problem” and “can you get here in less than 10 minutes.”

The documents say Mercado gave a statement to detectives acknowledging he met with Nunez and provided him a .22-caliber pistol.

Since that interview, detectives have been unable to locate Mercado, who moved out of his apartment in Oak Harbor. The gun has also not been recovered. Detectives believe it was tossed in the ocean after Johnson’s murder.

Prosecutors have obtained an arrest warrant for Mercado and have requested he be held on $5,000 bail. He faces up to a year in jail if convicted.

“I’m astounded that this is the first case,” said Shari Mattson-Cooper, the victim’s grandmother.

She said she thought it might be her grandson’s “way of helping society.”