"They've tried to point a finger at people more senior than where we found the decisions were made," Pickering, whose career spans four decades, said of Clinton's critics.
The Accountability Review Board, which Pickering headed with retired Adm. Mike Mullen, the former chairman of the Joint Chiefs of Staff, did not question Clinton at length about the attacks but concluded last December that the decisions about the consulate were made well below the secretary's level.
Pickering and Mullen's blistering report found that "systematic failures and leadership and management deficiencies at senior levels" of the State Department meant that security was "inadequate for Benghazi and grossly inadequate to deal with the attack that took place."
Pickering's defense of his panel's conclusions, however, failed to placate Republicans who have called for creation of a special select congressional committee to investigate the Sept. 11, 2012, assault on the U.S. diplomatic mission that killed four Americans, including U.S. Ambassador Chris Stevens.
The top Republican on the House Oversight and Government Reform Committee said he wants sworn depositions from Pickering and Mullen, and promised to make that request on Monday.
"This is a failure, it needs to be investigated. Our committee can investigate. Now, Ambassador Pickering, his people and he refused to come before our committee," said Rep. Darrell Issa, R-Calif., the panel's chairman.
Pickering, sitting next to Issa during an appearance on one Sunday show, said the chairman was lying and that he was willing to testify before the committee.
"That is not true," said the former top diplomat who has served in Republican as well as Democratic administrations.
In a separate interview, Pickering said he asked, via the White House, to appear at Wednesday's session. He said he could have answered many of the questions lawmakers raised, such as whether U.S. military forces could have saved Americans had they dispatched F-16 jet fighters to the consulate, some 1,600 miles away from the nearest likely launching point.
"Mike Mullen, who was part of this report and indeed worked very closely with all of us and shared many of the responsibilities directly with me, made it very clear that his view as a former chairman of the Joint Chiefs of Staff that there were nothing within range that could have made a difference," Pickering said.
Republicans and Gregory Hicks, the former deputy chief of mission in Libya, have questioned why the military couldn't move faster to stop the two nighttime attacks over several hours. Hicks, who testified before the House Oversight panel this past week, said a show of U.S. military force might have prevented the second attack on the CIA annex that killed security officers Tyrone Woods and Glen Doherty.
Mullen's successor as Joint Chiefs chairman, Gen. Martin Dempsey, and former Defense Secretary Leon Panetta told a Senate panel on Feb. 7 that they didn't have enough intelligence about what was happening, did not know where the ambassador was and F-16s would have been the wrong aircraft.
"You can't just willy-nilly send F-16s there and blow the hell out of a place without knowing what's taking place," Panetta had told the Senate Armed Services Committee on Feb. 7.
At the hearing last Wednesday, Hicks and two other State Department witnesses criticized Pickering and Mullen's review. 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.
"I was surprised today that they did not probe Secretary Clinton in detail," Sen. Kelly Ayotte, R-N.H., said, of the review board.
The hourslong hearing produced no major revelation but renewed interest in the attacks that happened during the lead-up to the November 2012 presidential election.
Even so, Republicans showed little interest in dropping their investigation into what happened at the consulate, what might be done to prevent future such attacks and what political calculations went into rewriting talking points the U.S. Ambassador to the United Nations, Susan Rice, used on news shows.
A series of emails that circulated between the State Department and the CIA led to weakened and, in some cases, erroneous language that Rice used to describe the assault during a series of five television interviews the Sunday after the attacks.
"I'd call it a cover-up," said Sen. John McCain, R-Ariz.,who renewed his call for a select committee to investigate. "I would call it a cover-up in the extent that there was willful removal of information, which was obvious."
Rep. Mike Rogers, R-Mich., chairman of the House Intelligence committee, said he expects more State Department officials to step forward and testify.
One Republican eyeing a White House run, Sen. Rand Paul of Kentucky, told an audience in Iowa that he thinks the Benghazi attack "precludes Hillary Clinton from ever holding office."
Democrats said Republicans were looking to weaken her ahead of a potential 2016 campaign.
"This has been caught up in the 2016 presidential campaign, this effort to go after Hillary Clinton," said Sen. Dick Durbin, D-Ill. "They want to bring her in because they think it's a good political show and I think that's unfortunate."
Rep. Adam Smith of Washington state, the top Democrat on the House Armed Services Committee, said the congressional probe "has just become a very, very partisan-focused, scandal-focused attack by the Republicans investigating this."
Pickering declined repeated opportunities to criticize Rice's now-debunked talking points that suggested the attacks were not terrorism.
"That was not in our mandate," Pickering said. "We were looking at the security, security warnings, security capacity, those kinds of things."
Democrats similarly did little to defend the mistaken talking points.
"This is one instance where you know it was what it was," said Sen. Dianne Feinstein, the California Democrat who heads the Senate Intelligence Committee.
"There was no question this was a terrorist attack," Smith said.
Pickering spoke with CNN's "State of the Union," NBC's "Meet the Press" and CBS' "Face the Nation." Issa and Feinstein spoke with NBC. McCain spoke to ABC's "This Week." Ayotte and Durbin were on CBS. Smith spoke to "Fox News Sunday."