The Camera Fiend by E.W. Hornung

His overwhelming horror was not alleviated by a moment's doubt. He marvelled rather that he had never guessed what he had done. The walking in his sleep, the shot that woke him, the first words of Dr. Baumgartner, his first swift action, and the warm pistol in his own unconscious hand: these burning memories spoke more eloquently than any words. They would have told their own tale at once, if only he had known the man was dead. Why had he been deceived? It was cruel, it was infamous, to have kept the truth from him for a single instant. Thus wildly did the stricken youth turn and rend his benefactor for the very benefaction of a day's rest in ignorance of his deed. The doctor defended himself firmly, frankly, with much patience and some cynicism. Pocket was reminded of the state he himself had been in at the time. He also might have been a dying man, he was assured, and could well believe on looking back.

Baumgartner had actually opened his lips to tell him the truth, but had checked himself in sheer humanity. Again the boy could confirm the outward detail out of his own recollection. To have told him later in the morning, the doctor went on to say, with an emphasis not immediately understood, could have undone nothing. He acknowledged a grave responsibility, but rightly or wrongly he had put the living before the dead.