Forensic Toxicology

For many centuries, poisoning has been a popular method of murder.   One reason is that almost any natural substance in the right dose can be poisonous, and many poisons mimic common medical diseases, leading physicians to believe a victim died of natural causes. 

Toxicology is important not just for an investigation in which foul play is suspected.   It is equally essential for determining accidental deaths and suicides—and even for substance abuse while on the job.  A toxicologist may be called on to test for anything from arsenic to poisoned gas to GHB to prescription drugs.

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"The American Chemistry Society has said there are about 21 million registered compounds," says Dr. Robert Middleberg of National Medical Services, the world's foremost independent toxicological testing laboratory, which tests for more than 3,000 of those compounds. He suspects the number of poisonings each year are underestimated.

While toxicologists need "symptoms, signs, and a good case history" to narrow down the diverse range of possible substances suspected in a death, sometimes it becomes a matter of systematically eliminating them by category.

Marilyn Monroe

There are several common substances to look for to determine whether a death is a suicide or an accident.   When Marilyn Monroe was found dead from an overdose of Nembutal and chloral hydrate in 1962, a psychological analysis was done as well as a toxicological screening.  These tests suggested that she fit the profile for frequent suicidal depression, even though they did not take into account the many recent positive events going on in her life at the time of her death. Very controversially, accidental death was ruled out, although the drugs used seemed obvious, since the packages were on her nightstand. While there were a number of conspiracy theories, the physical evidence suggests accidental death was the only way to explain the autopsy results.

A popular poison for suicide is carbon monoxide from a car engine, although drug overdoses or mixed doses of domestic medications are also widely used.   Accidental deaths can result from overdoses of drugs such as opium, hyoscine, morphine and heroin.  Examples of poisons that have been commonly used for murder are aconitine, atropine, strychnine, thallium, antimony, arsenic and cyanide. 

Forensic Science Glossary

The history of forensic toxicology goes back about 200 years, but before reviewing it, let's first define what this branch of science actually is. Technically speaking, John Brenner's Forensic Science Glossary defines toxicology as the study of poisons, but it also covers the detection of foreign substances in the body that can have a toxic effect, such as alcohol, industrial chemicals, poisonous gas, illegal drugs, or drug overdoses.  Sometimes a toxicological procedure involves analyzing a blood or urine sample, or a strand of hair.  Other times it requires a full autopsy in which tissue samples are removed from various organs.  A living person may be tested for a suspected substance with a basic kit, such as a breathalyzer for detecting alcohol levels, and if that registers a positive result or if symptoms show something different, a more sophisticated analysis may be required.

Dr. Hermann Boerhaave

The first person to suggest a chemical method for the detection of poisons, according to Thorvald Jurgen in The Century of the Detective, was Dr. Hermann Boerhaave.   His method was relatively unsophisticated, consisting of placing substances suspected of containing poison on red-hot coals, then testing the subsequent odors.  In the early stages of forensic toxicology, arsenic was the most common poison of choice.  It was known as the "poison of poisons" and "inheritance powder," since many relatives used it to dispatch some aging patriarch.

One such case that went to trial illustrated some odd methods for making a forensic examination.   Colin Evans described it in The Casebook of Forensic Detection, stating that it was the first murder trial to actually feature toxicological testimony from medical experts.

The incident occurred in England in 1751 and was the result of a typical domestic situation.  Mary Blandy agreed to marry Captain William Cranstoun, a man of supposed wealth and position, but he already had a wife in Scotland.  He also did not have as much money as he claimed.  When he asked his Scottish wife to issue a statement that they were not married, she took him to court—a scandal that thoroughly embarrassed Mary's well-to-do father.  He tried to oust the bum, but Mary was in love and began to meet with the good captain secretly.

When he fell deeper into debt, he told Mary he knew of an herbalist who might assist them in "settling" her father's estate on them.   Cranstoun put this powder in the older man's tea, but to no real effect.  So he gave Mary the powder and instructed her to keep administering it in small doses.

Arsenic has different effects in different degrees of ingestion.   It is absorbed from the bowel into the bloodstream, writes Sylvia Barrett in The Arsenic Milkshake, and then goes into the organs.  The liver, which takes up toxins, gets most of the brunt of its effect, but when delivered in one large dose, it quickly hits the brain as well, causing damage there and in the spinal cord.  When delivered to someone in smaller doses over a period of time, the poison affects the peripheral nerves, stripping their insulating sheaths and causing them damage.  The person will feel a prickly heat, like hot needles, and the skin may blister.  They will also suffer severe headaches, nausea, numbness, and general weakness.

Mr. Blandy grew ill with gastric distress, which sent the servant to examine his food.   She found the white powder and engaged an apothecary to examine it.  He wasn't sure, but the servant told the old man of her suspicions that Mary was using arsenic on him.  Mary tried to destroy the powder by throwing it into a fire, but the servant rescued it and kept it.  Nevertheless, Blandy allowed his daughter to continue to prepare his food.  Within a short period of time, he died.

Cranstoun fled to Europe, but Mary was caught on her way out of town and arrested. 

Her trial in 1752 was brief.   It's notable in the history of toxicology in that four doctors who had observed Blandy's organs at autopsy testified about the substance that killed him.  They said the "preserved quality" of these remains were highly suggestive of arsenic poisoning.  One doctor had applied a hot iron to the powder that the servant had rescued from the flames and analyzed it by smell — a poor test.

What probably carried the day, more than anything the doctors said, was the servant's testimony about the food and the powder.   Mary claimed it was meant to improve her father's dour temperament, but her actual behavior when caught said otherwise.

The jury found her guilty of murdering her father and sentenced her to death.   On April 6 that year, she was hanged.

Fortunately, the state of "science" regarding poisoning made some advances beyond the rudimentary sensory "tests" the experts at this trial had performed.   Yet their attempt to give a sophisticated response had started the ball rolling toward paying serious attention to standardized forensic detection.