Arrest over leaked video of US gunship attack - ABC News (Australian Broadcasting Corporation). The video really is shocking - especially since nothing I could see (except the camera) looked remotely like a weapon to me. But the former soldier who has spoken out against attacking the rescue truck actually defends the original shooting. He appears to accept the identification of weapons in the group and also claims that his team did find some on the ground when they arrived (but doesn't say how many).
It would be useful to the US military if they could support these claims (and/or show that the victims were in a well announced no-entry combat zone). Since they haven't done that my guess is they can't - and so the charge of murder still stands.