"No, I was up on that hill. In fact, our helmets have recording devices. It's how we knew who killed Alpha..." Kappa explained. He removed his helmet and handed it to Shepard, who put it on. A short video clip played, showing a sniper rifle aimed at the camp, Alastair entering the building and then the missile firing.
OOC: if you're wondering how this works out, Kappa recorded it on Upsilon's helmet.