The State Department inadvertently released the name of a CIA source who is suspected of being the main plotter behind the 1988 Lockerbie, Scotland airline bombing, and the House Select Committee on Benghazi republished the mistake this week.

The CIA told Congress that the name of the alleged secret agency source was not considered by the agency to be a major secret.

The name was mentioned but then partially redacted by the State Department from an email received on Hillary Clinton's private server.

At issue is Moussa Koussa, a one-time intelligence chief for Libyan dictator Muammar Gaddafi, whose name was mentioned in an email Clinton received four years ago from her close confidant Sidney Blumenthal.

Scroll down for video

Moussa Koussa was mentioned in an email Clinton received four years ago, he was widely suspected for many years of having been behind the bombing of Pan Am Flight

The Benghazi committee released this email that the State Department neglected to sanitize, including the name of Moussa Koussa who was a CIA source suspected of being behind the Lockerbie bombing

Koussa was widely suspected for many years of having been behind the bombing of Pan Am Flight 103, which killed 243 passengers, 16 crew, and 11 people on the ground.

Yahoo News first reported on the email snafu.

A spokesman for the Benghazi committee blamed the State Department, saying it had 'failed to redact' Koussa's name from the subject line of the email in question, even though it was covered up in the rest of the message.

State Department spokesman Mark Toner acknowledged the mistake on Tuesday, calling it 'human error.'

Republicans, who are trying to show Clinton mishandled classified information while secretary of state, have argued that Koussa's name should not have been included in the email.

But the CIA, weighing in after the Republicans made their accusation earlier this month, has told lawmakers that Koussa's name was not classified, according to correspondence between the spy agency and officials of the House of Representatives panel set up to investigate the Sept. 11, 2012 attacks on a U.S. diplomatic facility and nearby spy base in Benghazi, Libya.

The State Department considered redacting his name a priority on privacy grounds, not for any national security reason.

But Gowdy said Monday that the State Department's mistake exposed the 'name of a [CIA] human source,' making it 'some of the most protected information in our intelligence community.'

December 1988: Some of the wreckage of Pan Am Flight 103 after it crashed onto the town of Lockerbie in Scotland, on December 21, 1988. The Boeing 747 'Clipper Maid of the Seas' was destroyed en route from Heathrow to JFK Airport in New York when a bomb was detonated in its forward cargo hold

After months of delays and political machinations, Clinton is scheduled to appear before the House Benghazi committee on Thursday to answer questions about her handling of the 2012 attacks, her controversial private email server, and the Obama Administration's Libya policy.

WHO IS MOUSSA KOUSSA? Moussa Koussa was interrogated byScottish prosecutors in 2011 in connection with the Lockerbie bombing after he moved to the UK and claimed asylum. Libya's rebel leadership at the time demanded his return to the north African country to face trial for war crimes. He had been Muammar Gaddafi's intelligence chief from 1994 to 2009. Koussa never returned to Libya. Instead he was seen by the west as a vital part of its intelligence apparatus, being the first to unravel the knot of Islamist groups in Sudan, Niger, Mali, and Chad during the 1990s that would later coalesce as al Qaeda. Former CIA director George Tenet has credited him with being the first intelligence leader to issue an Interpol 'red notice' – an international arrest warrant – for Osama bin Laden. Although he was valued by U.S. and British intelligence as an al-Qaeda-hunter, Koussa was also at the center of rehabilitating Gaddafi's image internationally. In the end his use as an intelligence source outweighed his allegiance to the former dictator: The U.S. dropped all financial sanctions aganist him in 2011 just one day after he defected to the UK. He didn't stay there long, however. Koussa now reportedly lives in Doha, Qatar. Advertisement

After reviewing Clinton's emails in response to Freedom of Information requests, the State Department made numerous redactions, declaring that in some cases, the material should be considered classified.

Earlier this month, in a reference to Koussa, the Bengahzi committee chairman, Republican Trey Gowdy, complained that Clinton, the front-runner in the Democratic presidential campaign, had received an email on her private server in March 2011 with the name of 'a human source.'

That represents 'some of the most protected information in our intelligence community, the release of which could jeopardize not only national security but also human lives,' Gowdy said.

'Armed with that information, Secretary Clinton forwarded the email to a colleague - debunking her claim that she never sent any classified information from her private email address,' he added.

OOPS: House Rep. Trey Gowdy, who leads the congressional panel on the Benghazi attacks, released an email – which the State Department had neglected to sanitize – mentioning the name of a CIA source allegedly tied to the Lockerbie bombing

Sources familiar with the redaction process said the State Department did redact Koussa's name from the email in question but that the department had done this as part of standard practice to protect the privacy of individuals and not because the department considered the data classified.