Innocent people are killed all the time in conflict, its just how the pieces fall.
Its covered up because the backlash from people who either don't understand or chose to turn a blind eye to the reality that is war is outrageous. Its not worth coming clean because people refuse to look past a casualty to understand why it happened and what lead up to it.
It sounds terrible, but its true - a group of men of Arab background, walking through a LIVE war zone, with bags shouldered just as you would an assault rifle. Its going to draw negative attention in the form of cross hairs. Our enemies in Iraq don't open fire on our troops. They conceal IEDs and blow themselves up, it makes approaching suspicious individuals out of the question. Sadly, that narrows the window of deciding whether it is friend or foe.
I have faith in my government, their job is to ensure my safety and livelihood, and they are damn good at it. They could show up at my house and drag me off to a hole in the ground and put a bullet in my head. I don't give them a reason to though, I don't place myself in a position to draw that form of attention. If I whip out a lighter and reach for my shoe on my flight to Seattle, that would give them reason.
No system is perfect, U.S. soldiers have killed in cold blood before and been court marshaled and sent off to prison. This was not a cold blooded killing, there was substantial reason to suspect that the people killed could have been insurgents.
As for the comments in the video, draw your own conclusions. I have a handful of friends that have done one or more tours in the sandbox. One of them has PTSD so bad that he is dangerous to awaken. He wife made the mistake of tapping his shoulder to wake him up - he had her on her back with his hands around her throat, ready to kill her before his conscious mind even caught up.
War destroys the mind, people never come back the same.