The Man Who Loved Too Much

While Conan and Kogoro are heading to the store to go grocery shopping, they find a crowd in front of a house they're passing by. In the middle of a badly ransacked room is a man bleeding from the head. According to the couple that lives in the house, they happened to run into the man, who was a thief. They apparently killed him when he attacked them and they fought back. It seems like a clear case of self defense, but...