Three years after the Benghazi terror attack, the families of the victims are getting increasingly frustrated over the long wait for justice -- and answers.

"I am not going to let this die. Justice must prevail," Charles Woods, the father of former Navy SEAL Ty Woods, told Fox News.

His son was killed defending the CIA annex in 2012, one of the four Americans who died in the attack. Like other family members, Woods lives with painful reminders of his loss -- and is still waiting for some resolution.

The day after the Sept. 11, 2012, attack, President Obama vowed: "Make no mistake -- justice will be done."

Yet three years later, only one person has been arrested and charged by the U.S. -- Ahmed Abu Khattala, who was captured last June in Libya by a U.S. special ops team. He is facing an 18-count indictment.

Woods is critical not only of the administration's efforts but also the lack of public progress by the Benghazi Select Committee. That committee is tentatively planning to hear from former Secretary of State Hillary Clinton on Oct. 22; Chairman Trey Gowdy, R-S.C., vowed Thursday she will not be the last witness.

Also killed in the attack were foreign service officer Sean Smith, Ambassador Chris Stevens, and Glen Doherty, a former Navy SEAL doing security and surveillance work for the CIA.

"I need to know why my son was killed in Benghazi," Pat Smith, mother of Sean Smith, told Fox News in August. She added, in reference to Clinton's personal email system, "I want to know what's on that server."

Woods said his resolve was strengthened Thursday, on the eve of the anniversary, after seeing a road sign by chance while driving along Highway 213 near Oregon City. Ty graduated from Oregon City High School.

"I am in Oregon getting my other kids registered for college. And driving down the freeway, I saw this sign for 'Fallen Hero. Memorial Highway. Tyrone S. Woods U.S. Navy.' I pulled over, and took a picture as the tears went down my cheeks. He is my son," he said, vowing "justice must prevail."

Woods' unanswered questions include: "As a father, everyone knows there were military assets -- why were they not used in this case? SEALs will die rescuing their own. There was a very important conversation that night, what was said between Hillary Clinton and our commander in chief?"

Other family members voice similar frustrations.

Michael Ingmire, Sean's uncle, urged the government to, "Do. Your. Job."

"Get to the truth -- stop playing games," he said. "We're going on a third-year anniversary and it feels like a decade."