Minerals

Minerals have played many important roles in the world of forensic science, from forensic geology used in criminal identification and crime scene investigations, to forensic toxicology and the study of poisons.

Historically, metal-based mineral poisons were commonly used as murder weapons, with arsenic a favorite. In fact, arsenic was often referred to as "inheritance powder" for its efficacy in hastening the demise of wealthy relatives. In the eighteenth century, the Dutch physician Hermann Boerhaave (1668–1738) was the first expert witness to use basic forensic toxicological methods as the basis for testimony at a murder trial. In this case, Mary Blandy was encouraged by her fiancé to use a powdered preparation in order to get the money from her father's estate (he was very much alive at the time). She dutifully put the white substance into her father's food; he became ill. The servants became suspicious. One of the servants found the white powder and took it to a local apothecary for examination, where the hypothesis was arsenic. The servant relayed her concerns to her employer, who dismissed them, and not long after, was dead. Mary was tried for murder, and four medical toxicologists served as expert witnesses. They noted that the appearance of Mr. Blandy's organs at autopsy was suggestive of arsenic poisoning. Boerhaave reported that he had taken some of the white powder saved by the servant, treated it with a hot iron and smelled it (not a safe test for poisons, by any means). The smell was that of arsenic. Equally important was the testimony of the servant, who was able to describe the white powder that she had observed Mary putting into her father's food. Mary Blandy was found guilty of murder, sentenced to death, and hanged shortly thereafter. This trial set the stage for development of forensic toxicological methods for detection of metal-based (and other) poisons.

In 1911, a forensic method for determining the quantity of metal-based poisons in internal organs was developed by the English physician William Willcox, who was particularly interested in arsenic poisoning. He ran several tests for arsenic, and then used this method to determine how much arsenic was in each of the internal organs of Elizabeth Barrow, a victim of murder by poisoning. His method was used as the basis for far more sophisticated toxicological testing, which can now determine the amount of arsenic down to the microgram (one one-millionth of a gram) in both the human body and in soil.

After the middle of the twentieth century, thallium, a new metal-based poison, was popular for use in rat poison. Although it was banned from commercial use in 1984, it remained readily available in rat poison for at least another decade. In August 1991, Robert Curley developed a barrage of confusing symptoms and was repeatedly hospitalized. The cluster of symptoms included uncontrollable vomiting, abrupt hair loss, numbness of the extremities, general weakness, and burning skin. Shortly before his death in September 1991, he became combative, agitated, and aggressive; at that point, heavy metal exposure was hypothesized. A battery of tests revealed markedly increased thallium levels in his system.

Curley worked in a chemistry laboratory at Wilkes University in Wilkes-Barre, Pennsylvania. Five bottles of thallium salts were found in a stockroom there, although none of his coworkers became ill or evidenced any signs of accidental thallium exposure. Upon Curley's death, an autopsy was performed; it revealed extremely high thallium levels, confirming intentional poisoning, and leading to a ruling of homicide. During the investigation, the Curley home was examined, and several thermoses tested positive for thallium. Curley's widow reported that her husband brought iced tea to work in the thermoses daily. Curley's widow and her daughter by a previous marriage were found to have slightly elevated thallium levels, but they were well below the toxic range. Curley's widow sued the university for wrongful death. Upon further investigation, it was found that she had collected more than one million dollars from a car accident involving her first husband, and had also gained nearly three hundred thousand dollars in life insurance proceeds after Curley's death. At that point, she became a suspect, and the local criminal authorities requested exhumation of the body in order to perform more sophisticated testing.

Frederic Reiders, of National Medical Services, agreed to run forensic toxicology tests on Curley's hair shafts, toenails, fingernails, and skin. From the length of the victim's hair, Reiders was able to create a timeline extending 329 days before Curley's death. He used atomic absorption spectrophotometry to record thallium levels at different times. The surprising conclusion was that Robert Curley had been systematically exposed to thallium, through ingestion, for a period of nine months before his death. There was a sharp spike several days before his death, indicating intentional poisoning. Hair from other parts of his body, as well as the skin, fingernail, and toenail samples, all supported the conclusions reached by Reiders after testing the head hair. It was further determined that the valleys, corresponding to drops in thallium level, occurred whenever Curley was away from home (or in the hospital). When confronted with conclusive evidence, Curley's widow plea-bargained and confessed to poisoning her husband in an effort to gain his life insurance proceeds.

As testing for metal-based poisons has become progressively more conclusively detectable, the criminal use of these substances as a "murder weapon" has dramatically decreased in favor of plant-based toxins.