http://en.wikipedia.org/wiki/2012_Benghazi_attack
The main issue appears to be that the administration had information and evidence they did not disclose to congress before it was reported in the newspapers and the slow response.
Those are symptoms of an administration trying to come up with a PR strategy in order to avoid being blamed, or having to blame someone they posted.
Because they kept trying over and over again to get a handle on things, and held back information repeatedly until it was forced from their tight fist, many are wondering what else they know that they were successful in hiding.
While hindsight is 20/20, many believe that there was enough information to make a better decision prior to the event, implying that the decision wasn't mere ignorance, but active neglect, and not at lower levels but at Clinton's and possibly Obama's level.