House investigators talking to new Benghazi whistleblowers

President Obama's counterterrorism adviser, John Brennan, asked Libya's president for help in tracking down the militants who attacked the consulate. Elizabeth Palmer speaks with a senior Libyan Army officer about where the militants might be.

CBS News has learned that multiple new whistleblowers are privately speaking to investigators with the House Oversight and Government Reform Committee regarding the Sept. 11, 2012 terrorist attacks on the U.S. compounds in Benghazi, Libya.

The nature of the communications with the whistleblowers and their identities are not being made public at this time. But in response, the Oversight Committee yesterday sent letters to the three federal agencies involved: the CIA, the Defense Department and the State Department.

The letters make the case for the whistleblowers to be able to share sensitive or classified information with their own attorneys, and ask for each agency's official description of the legal steps that process must follow. The letters also state that additional witnesses may be "compelled by subpoena to give testimony."

Four Americans, including U.S. Ambassador Christopher Stevens, were killed in the Benghazi attacks seven months ago. No arrests have been made.

Various Republican members of Congress and congressional committees have been investigating several facets of the incident including lax security, the U.S. response during the attacks, and the Obama administration's initial statements blaming a "spontaneous protest" gone awry, rather than planned terrorist attacks. A State Department board of investigators issued a series of recommendations on ways to try to avoid a similar tragedy in the future, and the department is implementing them.

The Defense Department declined comment about the new letters from Congress saying it would be inappropriate to discuss the matter. The CIA and State Department also had no immediate response.

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    Sharyl Attkisson is a CBS News investigative correspondent based in Washington.