Quote Originally Posted by Acanous View Post
Honestly I'd expect any commissar to do the same. Trying to execute a space marine for dereliction of duty is very, very close to Heresey. The Emperor himself said "They shall know no fear"
I think it might be more accurate to say that they wouldn't do it because Commissars are attached to the IG command structure, and thus have no authority over any other organisation. Even the Imperial Navy has it's own Commissars posted aboard ships, and Marines have Chaplains who pretty much fulfill the same role.

I suppose there are unlikely situations where there is no one else around to hold the Marine to account, a Commissar might make it his business depending on how brave they were.... But if a Marine is doing something that warrents an execution, chances are that he's already a Renegade (and thus will soon have his entire Chapter on his heels looking for blood...) or is doing something already investigated by the Inquisition and cleared (certain blood rites performed by guys like the Blood Angels, for example, or a Space Wolf Wulfen 'mutant').

The only alternative would be for dramatic reasons, like the Marine protagonist of a novel who knows something that no one else does, and acts on it for the Greater Good and is pursued by a Commissar. He'll eventually be vindicated for saving lives, etc, but in the mean time the Commissar is acting in the right.