The Pimlico Mystery

Within the Victorian era, poison was the first choice of many murders. Deaths dating back to that of Napoleon Bonaparte (1821), suggest that toxic substances such as Arsenic, Cyanide and Strychnine all proved popular with the United Kingdom. One case however, which changed the whole perspective of murder by poison is that surrounding the Pimlico Mystery. A wealthy grocer, a young and beautiful French wife and a love triangle involving a reverend could have been a simple suicide, however the events that unfolded casted doubt on this death. Is it possible to poison someone without showing any evidence of the toxic product being consumed?