Augustin Dufosse is a non-canonical character who was created for the 2004 ITV adaptation of "The Murder at the Vicarage". Played by Herbert Lom, he plays the same role as Dr Stone in the original novel but has a very different background. He is addressed as "Professor" and stays as a guest at Old Hall. Unlike Stone who is conducting an archaeological excavation at Old Hall, Duffosse is studying and publishing articles about English country houses for a magazine.
As Miss Marple had seen him emerging from the woods behind the vicarage around the time of the murder of Colonel Protheroe, he is questioned by Inspector Slack. His cover is blown when Slack discovers that the magazine he claims to work for closed down before the war. He confesses to Slack that he is at Old Hall with his accomplice Joan Hargreaves in order to avenge his grandson "Henri". Henri had been in the French resistance during the war. Protheroe had been in charge of supply drops to the resistance members in Henri's region during the war. One night, Henri and Joan had waited for a scheduled drop of a large sum of French francs but the aircraft dropped the load somewhere else. It turned out that Protheroe had been in league with one "Lacombe", another member of the resistance. Protheroe had diverted the flight to drop the money somewhere else so that Lacombe could pick the money up and divide the money between the two of them after the war. Lacombe later betrayed Henri and Joan to the Germans. Joan had escaped but Henri was executed. Dufosse and Joan had been staying at Old Hall in order to search for evidence of Protheroe's treachery.
Dufosse also confessed that he had been in the woods and had actually entered the vicarage study intending to shoot Protheroe but when he got in, saw that Protheroe had already been killed. He noted a pistol with a long barrel, and saw that the note Protheroe had been writing was at least half a page long. Miss Marple and Slack later used these pieces of testimony to connect the crime to Lawrence Redding.