The attack on the American diplomatic mission in Benghazi, Libya, that killed our ambassador and three other Americans demands an independent investigation free from political agendas.

A lot of investigators are already looking into this tragedy – the FBI, Defense Department, State Department and Department of Justice are all involved. Rep. Darrell Issa, R-Calif., chairman of the House Oversight and Government Reform Committee, held a hearing – widely regarded as highly partisan – on security failures prior to the attack. The Senate intelligence committee plans to hold hearings starting Nov. 15.

Unfortunately, the Benghazi attack has been so thoroughly politicized that none of these investigations will be considered entirely credible.

The sad fact is that the Sept. 11 terrorist attack that lasted four hours and resulted in the murder of Ambassador J. Christopher Stevens and three other Americans has become the worst of political footballs. Republicans wasted no time in pointing fingers at the Obama administration for lax oversight and vacillating between blaming an anti-Islam film and calling it a terrorist attack. Obviously there were grave intelligence and operational failures, and the Obama administration’s actions have damaged its credibility in dealing with the attack.

As one example, emails received by the State Department and administration within two hours of the attack indicated an Islamic militant group was claiming responsibility. Secretary of State Hillary Clinton’s response that “posting something on Facebook is not in and of itself evidence …” fails to answer the bigger questions.

What did the administration know before, during and after the attack, and why wasn’t more done to secure the embassy in a country that had just undergone a bloody uprising and the capture and killing of dictator Moammar Gadhafi?

Stevens was widely regarded as one of the best U.S. diplomats in the Mideast. The question of why he was allowed to go to an obvious trouble spot with so little protection must be answered, along with accusations of some sort of administration coverup.

Last month, Sen. Joseph Lieberman, chairman of the Homeland Security and Governmental Affairs Committee, called for an investigation by the independent Inspector General’s Office. It was a good idea then and remains so. Or a truly bipartisan congressional panel could be created in place of panels dominated by Democrats or Republicans.

Americans, especially the families of the victims, deserve a thorough and independent investigation of the failures, and assurances that they won’t happen again.