Gregory Hicks, the deputy chief of mission in Libya at the time of the Sept. 11, 2012, attack on the Benghazi diplomatic post, described the day's events Wednesday.
Insurgents launched two nighttime attacks on the location, killing Stevens and three other Americans.
The hours-long hearing produced no major revelation while reviving disputes over the widely debunked comments made by U.N. Ambassador Susan Rice five days after the attacks and the inability of the U.S. military to respond quickly.
The session exposed bitter partisan divisions as Republicans who are pressing ahead with the investigation eight months after the attacks insist the Obama administration is covering up information and Democrats decry politicization of a national security issue.
A scathing independent review in December faulted the State Department for inadequate security at the mission, but it has not been the final word. Nor has congressional testimony from former Obama Cabinet officials and military leaders.
In a jam-packed hearing room where Republicans and Democrats furiously traded charges, the soft-spoken Hicks presented a lengthy recollection of the events and expressed frustration with a military that he argued could have prevented the second attack.
Hicks and two other State Department witnesses criticized the review conducted by former top diplomat Thomas Pickering and retired Gen. Mike Mullen, the former chairman of the Joint Chiefs of Staff. Their complaints centered on a report they consider incomplete, with individuals who weren't interviewed and a focus on the assistant secretary level and lower.
Hicks said that shortly after he was told Stevens was dead, unidentified Libyans called Hicks' staff from the phone that had been with the ambassador that night. These Libyans said Stevens was with them, and U.S. officials should come fetch him, Hicks said. Hicks said he believed Stevens' body was at a hospital at that point, but he could not be certain.
"We suspected we were being baited into a trap," Hicks told the committee, so the U.S. personnel did not follow the callers' instructions. "We did not want to send our people into an ambush," he testified.
Republicans at the hearing focused on the talking points used by Rice on the Sunday talk shows in which she said the attacks appeared to be associated with demonstrations in Egypt and Libya over an anti-Islam video.
Hicks, asked his reaction to the Rice's remarks on the talk shows, said: "I was stunned. My jaw dropped and I was embarrassed."
Democrats countered with a video clip of Director of National Intelligence James Clapper telling a Senate panel earlier this year that the hit on Rice was unfair.
"She was going on what we were giving her," Clapper said of the talking points.
Hicks insisted that the second attack in Benghazi could have been prevented if the U.S. military had scrambled jet fighters or sent in a C-130 cargo plane to scare off the insurgents with a show of force. He said he learned in conversations with veteran Libyan revolutionaries that they understood decisive air power after the U.S.-led NATO operation that helped oust Moammar Gadhafi.
Democrats pointed out that this contradicted the testimony of former Defense Secretary Leon Panetta and Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, who testified before a Senate panel on Feb. 7.
After the first attack, a security team left Tripoli for Benghazi with two military personnel. Hicks said four members of a special forces team in Tripoli wanted to go in a second wave but were told to stand down.
Pentagon press secretary George Little said Wednesday that the commander told the team leader to stay in Tripoli because the evacuation of U.S. personnel out of Benghazi was already beginning and the team would not arrive in Benghazi in time to provide any assistance.
Col. David Lapan, spokesman for the Joint Chiefs of Staff, said that by the time the team would have left Tripoli, the second attack in Benghazi was over.
Republicans on five House committees, in an interim report released last month, also said that "no U.S. government element refused or denied requests for emergency assistance during the crisis."
Rep. Darrell Issa, R-Calif., chairman of the Oversight and Government Reform Committee, insisted that the investigation is necessary despite Democratic and administration complaints.
Rep. Elijah Cummings of Maryland, the panel's top Democrat, challenged the select disclosure of information and comments from Republicans in the days leading up to the hearing.
The Associated Press contributed to this report.