Here was where the killers really lucked out. The AP photographer, though caught at unawares, who definitely had no "foreknowledge" of what was going down and at the worst expected a street demonstration, did not take cover, even as soldiers and Marines are trained to do when shooting starts. He was made of sterner stuff and held his ground, taking pictures of people he did not know killing individuals he did not recognize for reasons he would not have known about. This -- in the midst of "30 armed insurgents, hurling hand grenades and firing guns" -- as the Associated Press report says. And he continued to take photographs for a fairly long period of time, capturing not just a single photograph, but a sequence of them.
There's no gainsaying the logic in Wretchard's suspicions, and I haven't seen a convincing refutation. The debate continues.