Arsenic was, at one time, a very popular way to murder someone. It was the most common poison to factor in 19th century British murder trials, but it is also a particularly difficult cause of death to determine. In fact, most deaths by arsenic were attributed to natural causes, so for every murder trial involving arsenic, there were probably multiple cases in which the perpetrator got away with the crime.
Some poisons such as cyanide and strychnine work according to a strict timetable and dispatch their victims in a predictable manner. Arsenic, by contrast, is mysterious and shilly-shallying, behaving more like an infectious disease, so that the nature and length of the victim's suffering depends partly on their genetic make-up and general state of health. Death from acute arsenic poisoning can take anything from two hours to four days, although victims have been known to linger for a fortnight. For most, though, the misery lasts at least 24 hours.
To confuse matters further, human beings are capable of building up a certain tolerance to arsenic if they go about it carefully enough. In 1851, a community of peasants living on the Austria-Hungarian border were found to be taking arsenic in what would normally be lethal doses. They believed that the poison was good for their health and took it as a tonic, starting with a tiny sub-toxic dose and gradually increasing it.
Defense lawyers quickly seized on this to try to sow doubt in juries' minds. Was this case really murder? Perhaps the arsenic in the dead person's food or body had been self-administered for health reasons, only this time the victim had gone too far?
And there were other factors that made arsenic the go-to poison for those who wanted to hasten the death of someone they knew. Read about them in an excerpt from the book The Inheritor's Powder: A Tale of Arsenic, Murder, and the New Forensic Science at HuffPo Books.
(Image credit: Flickr user James Laing)