Charles Brockden Brown 
Edgar Huntly; or, Memoirs of a Sleep-Walker [EPUB ebook] 

Edgar Huntly, a young man who lives with his uncle and sisters (his only remaining family) on a farm outside Philadelphia, is determined to learn who murdered his friend Waldegrave. Walking near the elm tree under which Waldegrave was killed late one night, Huntly sees Clithero, a servant from a neighbouring farm, half-dressed, digging in the ground and weeping loudly. Huntly concludes that Clithero may be the murderer. He also concludes that Clithero is sleepwalking. (Wikipedia)