Crime Library: Criminal Minds and Methods

Forensic Toxicology

Black Widow's Best Friend

The next issue that forensic toxicology had to face with metal-based poisons was quantifying poisons.   It was no longer sufficient for a toxicologist to say that the amount of poison found was fatal without having numbers to back up the statement. 

In a murder case in 1911, Dr. William Willcox developed the first method for quantifying arsenic.   Frederick Henry Seddon was arrested for poisoning Elizabeth Barrow to steal her assets.  Scotland Yard authorized Willcox to make some tests.  He ran hundreds of weight tests for arsenic and then used his method to figure out how much arsenic was in each of the poisoned woman's internal organs.  He calculated the amount via body weight in milligrams.  His method was eventually refined over the years to the point of being able to detect the presence of arsenic down to the microgram (one millionth of a gram) in both the human body and in soil.

A famous case that involved the quantization of poisons was that of Marie Besnard, known as the "black widow of Loudun."   Besnard was accused of killing 12 people with arsenic, including her husband and her mother.  The string of deaths stretched across two decades, from 1929 until 1949.  Marie benefited in some manner from each of the murders, thus providing the prosecution with a motive.  All of the bodies were exhumed and high levels of arsenic were found in each one.  However, aside from the poison, the prosecution had only circumstantial evidence against Besnard. 

When the case went to trial the defense attacked the lab technique of the toxicologist, Dr. Georges Beroud, as careless.   This caused sufficient doubt that a second toxicological investigation was requested from a group of four toxicologists.  While this second investigation was being performed, the defense learned about a new theory: through anaerobic bacteria arsenic could enter the hair of a corpse from the ground.  This meant that the prosecution's experts would now have to prove that the arsenic in the bodies had not been introduced after burial. 

When complete, the second investigation also found significant levels of arsenic in the corpses.   However, Griffon, one of the toxicologists, had been careless in his determination of arsenic in hair.  The procedure required that the hair be subjected to radioactivity for twenty-six and one-half hours.  Griffon had only exposed it for fifteen hours, thus again calling the results into question. 

A third investigation was performed by another group of toxicologists, but when they could not disprove the defense's new theory, Marie Besnard was acquitted on December 12, 1961.

Not everyone has had such a clever lawyer.

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