Prosecutors in Island County have charged an Oak Harbor man in what is believed to be the first criminal case resulting from the gun background check initiative approved by voters nearly two years ago.

Prosecutors charged Mark A. Mercado with "unlawful transfer of a firearm" – a Phoenix Arms HP22 handgun.

In charging documents obtained by KING 5 and public broadcasting's Northwest News Network on Monday, prosecutors said Mercado sold his handgun on November 9, 2015.

It was used to murder 17-year-old John Skyler Johnson two days later.

“My grandson was murdered in my home here on the floor,” said Shari Mattson-Cooper, Johnson’s grandmother.

Sheriff''s investigators say Mercado sold the gun to 20-year-old David Nunez without seeking the required background check under Initiative 594.

That voter-approved measure requires buyers to receive a criminal background check when purchasing a gun from another citizen before a sale can move forward.

Nunez conspired with three friends to murder Johnson in an ongoing dispute. Nunez is now serving 25 years in prison.

Mattson-Cooper believes the case filing sends a strong message to private gun sellers.

“If it wasn’t for him maybe it never would’ve happened,” she said. “I don’t think I’m angry. I think I’m disappointed in our society,” she said of the relative ease it took for Nunez to purchase the gun.

But Mattson-Cooper was surprised to learn this is only the first case filed since I-594 started nearly two years ago.

“I’m astounded that this is the first case,” then she paused. “Maybe this is J’s way of helping society.”

Documents say Mercado left his job and moved out of Oak Harbor. Detectives do not appear to know his exact whereabouts. The documents state Mercado faces 364 days in jail or $5,000 fine, or both.