If true, this exceeds the boundaries of any moral codes agreed upon since the Dark Ages.
Perfectly legitimate for the US, even acting in a reserved Obama-ish way, to deploy waves of assassins from the CIA, SEALs, whatever, to kill whomever was involved. And make examples. Painful examples.
Frankly, the Libyan government should be doing this already, for an insult of this magnitude. And offering complete oversight to the State Department in advance, along with lead on any missions they would like.