Ashenden, by Somerset Maugham

This is a series of stories about Ashenden, a British agent during the First World War. Maugham tells us in his introduction that the book is based on his own experiences in the Intelligence Department, "rearranged for the purposes of fiction". Maugham defends this approach by arguing that in fiction, events can be made far more sequential and coherent than things usually are in real life, but it does mean that we are never quite certain how far the stories he tells actually occurred. As we would expect from Maugham, the book is beautifully written: his excellence as an author has rather been forgotten nowadays.
Most of the stories are set in neutral Switzerland, where Ashenden is based, though in the last story he finds himself in Petrograd at the time of the Bolshevik seizure of power in autumn 1917, but fails to make any impact on the course of events (which presumably mirrors Maugham's own experiences). In some of the stories not very much happens, but two of them stand out by being distinctly sombre. In one, Ashenden cold-bloodedly manipulates a woman in order to get her to betray her lover, an Indian nationalist agitator who has thrown in his lot with the Germans. In another, in even darker vein, his target is an Englishman living in Switzerland who is suspected of being in the pay of Germany. Ashenden eventually deceives him into venturing onto French soil, so he can be arrested and shot. This is not made any more palatable for Ashenden by the fact that he actually likes Caypor, the target, and his wife. When he receives the information that Caypor has duly been executed, Ashenden reflects that personal feelings must not be allowed to have any bearing on his work, but even so he is unable to stop himself thinking of the reality of a firing-squad:-
"He remembered a dreadful scene. Dawn. A cold, grey dawn, with a drizzling rain falling. A man, blindfolded, standing against a wall, an officer very pale giving an order, a volley, and then a young soldier, one of the firing party, turning round and holding on to his gun for support, vomiting. The officer turned paler still, and he, Ashenden, feeling dreadfully faint. How terrified Caypor must have been! It was awful when the tears ran down their faces ...."
Did Maugham himself witness such an execution, or did someone describe it to him? Or is it purely a product of his imagination? In any case, we are certainly a long way from James Bond's casual attitude towards death, are we not?