The reality of war is that while responsibility is shared, the ultimate responsibility goes with the person who pulled the trigger because they did not tell Gregory he was going to be executed.
The executioner does not want to kill Gregory, and neither do the other guards. The narrator, the executioner, comments on the brutality of war.
Even though his name was Gregory and some people on his side had killed scores of ours, even though we had left wives and children to go to war against him and his kind - but how can I explain? He was our friend. (186-8)
He is a friend to Gregory, and he tries to give him opportunities to escape, but Gregory does not take them. Despite the cruelty of the situation, the truth is that the guards could have tried harder. They did not tell Gregory that he was about to be executed.
[He] saw that we looked gloomy and he began to suspect that something was up. He tried talking to us, but he got no answers and then he stopped talking. (199-200)
When they had their chance, they did not tell Gregory that the execution order had been handed down. If they had, he might have actually attempted to escape. Instead of simply giving him opportunities, they should have realized that he saw them as friends and protectors and would not betray them. If they had, they could have saved his life.
IOANNIDES, PANOS (2011-08-15). GREGORY AND OTHER STORIES (Kindle Locations 186-188, 199-200). Armida Publications. Kindle Edition.