They are charging the senior officers with not fully investigating the matter, but they are having to grant immunity to a bunch of folks to try to find out what happened. Perhaps Lt. Gen. James Mattis should be added to the list of defendants, based on the lack of success of the investigation thus far.
And the government is STILL not certain enough of its case to commence the hearings. The government recently asked for (and was granted) postponements of the first two Article 32s that were scheduled.
If you want to read about a cover-up, read about My Lai. There was no cover-up in Haditha.