Who is Daniel Hickam from A Test of Wills and what is their importance?

Daniel Hickam is a former soldier home from war. The war was not kind to Hickam and he has returned a broken man, shell shocked and delusional. He spends most of his days drunk or lost in flashbacks about the war. Because he is relatively harmless and one of Upper Streetham's native sons, the villagers tolerate his antics. His testimony is key to the investigation because he contradicts what Mark Wilton has said about his whereabouts (opportunity), and it gives Wilton a motive for murder. Hickam heard the Colonel say he was calling off Lettice Wood's wedding.