Clearly opinions differ on the matter, but from my point of view, Damien did not "aid in an assault". He got dragged into and caught up in a shit-fest and did what he could to protect as many people as he could. He hauled the injured guard to safety, warned the MC to get clear, and (again, in my opinion) tried to keep the people inside from going out into danger.
But I freely admit that, given BD's track record so far, it's entirely possible that new evidence will come to light that shows my interpretation of the facts to be less than accurate.
"I have never killed any one, but I have read some obituary notices with great satisfaction." -- Clarence Darrow