WASHINGTON (CNN) - Top Republicans and witnesses ripped the Obama administration's response to last year's deadly attack on the U.S. diplomatic compound in Benghazi, Libya, calling key executive branch officials unresponsive in the critical hours after the assault and uncooperative in the investigations that followed.
Our goal "is to get answers because their families (of the victims) deserve answers," said California Rep. Darrell Issa, the Republican chairman of the House Oversight Committee, which heard from State Department "whistleblowers" at a hearing on Wednesday.
"The administration, however, has not been cooperative and unfortunately our (Democratic House) minority has mostly sat silent," he said.
Issa spoke prior to testimony from Eric Nordstrom, a former regional security officer in Libya; Mark Thompson, the State Department's acting deputy assistant secretary for counterterrorism; and Gregory Hicks, the former deputy chief of mission in Libya.
The attack last September 11 killed four Americans, including Ambassador Christopher Stevens.
Nordstrom said in written testimony that it was "inexplicable" that an internal State Department review ignored "the role senior department leadership played before, during, and after" the attack.
Doing so, he warned, "sends a clear message to all State Department employees."
Committee Democrats accused Republicans of playing politics with the tragedy.
"What we have seen ... is a full-scale media campaign that is not designed to investigate what happened in a responsible and bipartisan way but rather a launch of unfounded accusations to smear public officials," said Maryland Rep. Elijah Cummings, the top Democrat on the panel.
"It will be incredibly disheartening if the only reason that this hearing is being held is to level a partisan attack and try to grab headlines," said Rep. Matt Cartwright, D-Pennsylvania, in a written statement.
In the run-up to the hearing, Issa trickled out testimony from the witnesses in an apparent attempt to build anticipation for the session, one of several that have occurred in Congress focusing on security at the compound and the administration's response.
Among other things, Hicks has charged that the since the start of the attack, administration officials knew the culprit was al Qaeda and not -- as was initially claimed -- a spontaneous act that grew out of a demonstration over an anti-Islam film made in the United States.
"I think everybody in the mission thought it was a terrorist attack from the beginning," Hicks told investigators in interviews before the hearings.
Hicks, who was posted at the embassy in Tripoli, said during the session that he was told by the Libyan president soon afterward that elements with possible terror links were thought to be behind the assault.
He also said that Stevens told him in their final telephone conversation that the compound was "under attack." He said Stevens did not mention any prior demonstration.
Hicks' allegations echo a charge long made by Republicans: That following the attacks, the administration talking points explaining what happened were altered, making them untrue.
Republicans claim this change was made so the Benghazi investigation did not step on President Barack Obama's 2012 re-election campaign, which was in the final stretch at the time. Republicans sought to make the attack a campaign issue.
Hicks said his "jaw dropped" and he was "embarrassed" when the administration said initially that it believed the attack was an outgrowth of a demonstration over the film similar to those that had taken place earlier in Egypt.
"We want to find out who made this decision, who made the decision to change talking points in a way that caused the American people to be lied to," Issa told CNN's Chief Congressional Correspondent Dana Bash.
For its part, the State Department has joined congressional Democrats in accusing House Republicans of playing politics with the tragedy.
"This is not sort of a collaborative process where the committee is working directly with us in trying to establish facts that would help, you know, as we look to keep our people safe overseas in a very complex environment," State Department spokesman Patrick Ventrell said on Monday.
The State Department has flatly rejected GOP accusations that it has attempted to prevent would-be "whistleblowers" from speaking out.
Wednesday's hearing is another chapter in what has become an epic back and forth between Democrats and Republicans on Benghazi, partly stemming from televised comments after the attack by U.N. Ambassador Susan Rice.
She was the face of the administration in the days following the attack, and maintained in several media appearances its account of events -- that the assault on the compound was the result of a demonstration that turned violent.
Later, the administration called the Benghazi attack an act of terrorism. Rice and other officials said that her early comments relied on official talking points with the information the administration said it had at the time. Still, the initial statements and the resulting controversy cost her a likely nomination to succeed Hillary Clinton as secretary of state.
Some GOP members in succeeding months also sharply questioned Clinton over the administration's explanation of events and the state of security at the compound at the time of the attack.
Clinton said she took responsibility for the deaths, stating that as secretary of state, she was "in charge of the State Department's 60,000-plus people all over the world."
In January, Clinton testified for more than five hours before the House and Senate Foreign Relations committees. In her testimony, she acknowledged a "systematic breakdown" on Benghazi and said her department was taking additional steps to increase U.S. security at diplomatic posts.
At one point in the hearing, Clinton barely controlled her anger as she responded to a lawmaker who pressed her on the administration's post-attack storyline.
Critics have questioned the validity of continued congressional scrutiny, especially Democrats, who say Republicans are only interested in discrediting the administration and hurting Clinton's chances if she were to run for president in 2016.