Sibirtsev was not a man of doubt. He served as a marine and fought as a member of a boarding team. A few dozens of people found their end seeing his gun turned to them and it wasn't a problem at all for Captain to add a few more to the list. However, the words of the Commissar started to sink in and that was probably the first time Sibirtsev would hesitate. On the one hand, this is a typical test for a Coalition member checking subordination and loyalty, "kill or be killed". On the other hand, he was blamed for possibility of disobeying orders and it would be adequate to request the confirmation for execution.
Still, as the Commissar said no words on giving the gun, Sibirtsev clung on his first though, which is usually the right one, took the gun, by reflex checked the loadout and put it to head of a woman who would be now staying on her knees, face away from the gun.
Her weeping was nothing for a trained marine, he had seen far worse things. In a matter of few seconds he pulled the trigger and pierced the head of a poor victim with a beam of tachyons, leaving a small burn both in her skull and on the floor.
Without uttering a word, he offered a gun back to the Commissar. He knew that even if he failed the test, he did right, because that was the will of a Commissar, and thus - of the People and of the Party, and those are never mistaken.