Well what appears to have happened here is the Marine convoy was hit with a suicide bomb on a highway. The Marines say that they were then hit with small arms fire, which they returned. The Afghans appear to say that there was no small arms fire and the Marines just opened fire on civilian vehicles, apparently because they feared another VBIED.

If the Marines did get hit with small arms fire, there's no way to know if the Afghan civs were killed by Taliban or Marine fire, except by autopsies that will likely never be conducted.

Likely the films and camera memory cards were confiscated on the call of the local unit commander on scene, probably in fear of nasty pictures of dead civilians ending up in the news. Again, no way to know if the Marines were actually guilty, but they knew they would be blamed automatically in many media outlets. A clumsy move probably by a junior leader.