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