The Mark of Cain by Carolyn Wells

Of the General Public, there were few who doubted Landon's guilt. When no other explanation offered, it was plausible think that the dying man referred to his murderer as Cain. But when a man named Kane was shown to have motive and opportunity, when also, he was a bold and even impudent westerner, who could doubt that he was the murderer the victim meant to denounce?

Yet, some argued, ought he not to have the benefit of the doubt? Though he had an apparent motive, though he confessed to being in the vicinity at or near the time of the murder, that was not actual proof.