Rep. Trey Gowdy, R-S.C., told Reuters Thursday that he has subpoenaed the emails of "close to a dozen" people who worked for Hillary Clinton during her tenure at the State Department. Gowdy also officially requested that Clinton turn over her personal server for an independent investigation.

"We sent a subpoena to the State Department for emails from a number of individuals within the State Department, other than Secretary Clinton," including aides and even "aides to aides," said Gowdy, the chairman of the U.S. House committee investigating the 2012 Benghazi attacks.

He said that without the emails, no congressional committee investigating the Benghazi attack could claim to have conducted a comprehensive investigation. The State Department asked Gowdy to not disclose the names of people whose emails he requested, according to Reuters.

Earlier this month, Clinton was found that have used a personal email address connected to a private home server to conduct all government business while working as head U.S. diplomat from 2009 to 2013. Clinton finally turned over 30,000 work-related emails to the State Department for public record, but only after her team single-handedly deleted an additional 30,000 that she said were of personal nature.

Transparency advocates question why Clinton didn't allow an independent arbiter to examine the emails and decide which were appropriate to turn over, fearing Clinton could have whitewashed potentially incriminating evidence.

On Friday, Gowdy published a letter that he sent to Clinton's attorney requesting the former secretary of state to "relinquish" the server to a "neutral, detached and independent third-party," reported Fox News.

"Her arrangement places her as the sole arbiter of what she considers private and what is beyond the view of the public," Gowdy said in the letter.

Gowdy warned that if Clinton doesn't respond by April 3, he will advise House Speaker John Boehner to use the "full powers" of the House to take the "necessary steps," according to Fox News.

In a written statement released separate from the letter on Friday, Gowdy further voiced his concerns:

"An independent analysis of the private server Secretary Clinton used for the official conduct of U.S. government business is the best way to remove politics and personal consideration from the equation."

"Having a neutral, third-party arbiter such as the State Department IG do a forensic analysis and document review is an eminently fair and reasonable means to determine what should be made public."