Former Rep. Trey Gowdy, R-S.C., said Friday that it's been almost four years since details of Gen. Michael Flynn's phone call with the Russian ambassador were leaked to the media, but the question of who leaked the information remains.

"It's a 10-year felony," Gowdy told "Mornings With Maria" on Fox Business Network.

Gowdy, former chairman of the House Oversight and Government Reform Committee and a Fox News contributor, told host Maria Bartiromo that he was "struck" by how many people in the Obama administration had the power to request Flynn's name be unmasked.

OBAMA KNEW DETAILS OF FLYNN CASE, SHOCKING DOJ OFFICIAL IN WHITE HOUSE MEETING

"The undersecretary from Micronesia does not need unmasking power," he said, arguing that a leak investigation is difficult when so many people have access to the classified information.

Gowdy said the "serious crime" must be investigated and brought to a conclusion, especially considering how much effort was spent to bring charges against Flynn.

"So I ask the FBI again: how is your leak investigation going? I know how your Michael Flynn investigation went, I know the time and effort you spent to try to catch someone in a lie. How is your 10-year felony investigation going? It has been four years now," he argued.

Former U.S. ambassador to the United Nations Samantha Power sought to obtain Flynn's redacted identity using an "unmasking" request on at least seven occasions, according to newly declassified list of names released Wednesday -- even though Power testified under oath before the House Intelligence Committee that she had “no recollection” of ever making such a request even once.

While sensitive requests to “unmask” individuals – revealing their identity on a need-to-know basis after the intelligence community intercepts their communications – are not necessarily improper, the records raised new concerns over exactly who might have leaked details of the Flynn investigation to The Washington Post in January 2017.

The Biden campaign and former senior Obama administration intelligence officials have characterized the unmasking as routine after Biden's name appeared on a list of officials who requested the unmasking. The list also includes then-FBI Director James Comey, then-CIA Director John Brennan, then-Director of National Intelligence James Clapper, and Obama's then-chief of staff Denis McDonough.

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Biden, speaking to ABC’s “Good Morning America," first claimed, "I know nothing about those moves to investigate Michael Flynn." Pressed on the matter, Biden eventually acknowledged, “No, I thought you asked me whether or not I had anything to do with him being prosecuted. I’m sorry. ... I was aware that there was—that they asked for an investigation, but that’s all I know about it."

Fox News' Gregg Re contributed to this report.