I’m ignoring the claim because I don’t know the source and, in any event, am incapable of judging of what is possible or impossible for insurgents in Afghanistan to do.
At the very least, it seems prudent to wait until the investigation is complete and the evidence is tested before saying these Marines are guilty. Until then, I believe servicemen deserve the benefit of the doubt. I would give you the same presumption of innocence.
The source was the Marines themselves. Shooting went on from the VBIED hit almost to the gate at Jalalabad. People were killed / wounded throughout, and bullets were found the whole distance.
However, it never hurts to wait until the investigation is complete - the Marine one, not just the halted Army one. My main point is that this is one case where it might be best for BOTH sides of the argument to wait...it is definitely not a case of someone trying to build a career by slandering troops. There are solid reasons why the Army became very concerned, and why the Marine unit was pulled.