I'm new to the GM side of role play, and I just ran "Shadow of Madness" (not quite complete yet). We got to the Towering Glades and when the kill-team found the infant Vespids a fight broke out. Our Black Templar immediately tried to flame them (only natural) and our Space Wolf and Ultramarine tried to stop him. The Space Wolf attempted a grapple and failed. The Ultramarine had threatened to shoot the Templar if he tried to kill the Vespids. When it became clear the Space Wolf couldn't hold him, our Ultramarine fired a krak missile at the Templar. This caused a fate point to be burned for our Templar.
I am trying to decide how to deal with this situation, and I was curious how others have dealt with it (if at all). I've read a lot of 40k literature. I have read over 100 40k novels and most every source book the Black Library has produced. Page 278 of the deathwatch rulebook suggests that "acts of betrayal by fellow Battle-Brothers or trusted allies" could be a reason for insanity and I agree completely. I know that the hypno-indoctrination a battle-brother undergoes makes it difficult for him to even consider attacking a brother in a lethal way. Space marines may come to blows, but these are not intended to kill (however seriously they may fight). I believe that this is crossing a very big line for a character, and that the ramifications should be serious. I also know that every battle brother has taken an oath to the deathwatch, and I believe such an attack is probably at least a partial breach of this oath. I have been trawling through my many source books for a good quote on this (as I know I've read something that would directly affect what I'm discussing). I know the heresy books have addressed these difficulties, but I am still looking and hoping to find something more quickly than I can by simply re-reading the original trilogy.
My current assessment is that every battle brother that witnessed this should be given 1d5 insanity (5 marines). I think the perpetrator himself should gain 3d10 insanity. I'd like opinions on that, especially from GMs with a long history in 40k lore. I should also mention that one of my main goals as a GM in Deathwatch is to provide an authentic 40k experience, and I wouldn't mind in the least to have this character removed from the kill-team and sent back to Ultramar, although I'm still considering specific punishments.