Congressional Joint Economic Committee member U.S. Rep. Elijah Cummings, D-MD, prepares for a hearing in the Dirksen Senate Office Building on Capitol Hill, March 14, 2013, in Washington. Image credit: Chip Somodevilla/Getty Images

The top deputy to the U.S. ambassador killed during the Sept. 11, 2012 attack in Benghazi is set to deliver much-anticipated testimony today that could contradict the administration's explanation of the deadly attack that took the lives of four Americans.

Gregory Hicks, the deputy chief of mission for the U.S. in Libya, will appear before the House Oversight and Government Reform committee at 11:30 a.m. today. Hicks, a 22-year Foreign Service diplomat, became the highest-ranking civilian in Libya after U.S. Ambassador Christopher Stevens was killed in the attack, which the administration initially characterized as a spontaneous demonstration that turned into a violent attack.

Two other State Department officials - Mark Thompson, the acting deputy assistant secretary for counterterrorism, and Eric Nordstrom, the diplomatic security officer and former regional security officer in Libya - will join Hicks at the hearing titled: "Exposing Failure and Recognizing Courage."

The officials are also expected to be quizzed by committee members about emails showing administration officials may have deliberately downplayed what had transpired just six weeks shy of the presidential election.

Excerpts from a transcribed interview Hicks conducted with investigators from the Oversight and Government Reform Committee on April 11 show on the night of the attack Hicks repeatedly inquired whether any "big military" support was on the way to the consulate as the attack continued. While support was ultimately judged to be too far away to respond, Hicks claims that a special forces unit in Tripoli was prepared to board a flight to Benghazi but was told by military headquarters in Germany not to leave because they did not have the right authorization to do so.

"We fully intended for those guys to go [to Benghazi] because we had already essentially stripped ourselves of our security presence, or our security capability to the bare minimum," Hicks said, according to excerpts of the interview released by a Republican committee aide. "They were on their way to the vehicles to go to the [Tripoli] airport to get on the C-130 when he got a phone call from SOCAFRICA which said, you can't go now, you don't have authority to go now."

Hicks also says he immediately recognized the attack as the work of terrorists and he believes the Libyans would have been eager to grant permission for fast-moving U.S. air power to respond to scare off the assailants.

At the time of the April 11 interview, Hicks requested that his identity not be revealed, according to a Democratic aide privy to the agreement.

This week, Rep. Elijah Cummings, the top Democrat on the committee, criticized Republicans for releasing "snippets of interview transcripts to national media outlets in a selective and distorted manner to drum up publicity for their hearing."

A Republican aide refused to release the full transcript of the April 11 interview.