The early days of forensic science are depicted in Sandra Hempel’s The Inheritor’s Powder: A Tale of Arsenic, Murder and the New Forensic Science.

How did this book come about?

The idea came from an academic paper about criminal poisoning in the 19th century. The author looked at the difficulties the authorities had in proving that someone had been poisoned, and traced the advances in chemistry over the decades and the corresponding improvements in the way criminal poisoning was investigated. She also argued that the history of the development of forensic science in that century was really the development of forensic toxicology. This interested me because it brought together several of my areas of interest: the law, crime, forensics, the history of medical science, and the 19th century. When I began researching The Inheritor’s Powder, I was interested to see the name James Marsh constantly coming up. He developed a much more scientific, reliable test for the presence of arsenic, as a result of being called to give evidence in a murder trial in 1833. A young man had been accused of poisoning his wealthy grandfather in a small village southeast of London. When Marsh analysed some suspicious coffee, and also the victim’s stomach contents, he was taken aback at how rudimentary the tests then were, and this prompted him to spend his spare time over the next three years developing an alternative.

What surprised you the most as you wrote the book?

I did know that justice in those days was heavily weighted in favor of the prosecution, but I was still surprised at how many people were convicted of murder and executed on the flimsiest of evidence. With forensic science in its infancy and the role of detective nonexistent, a murder investigation was a cursory, hit-or-miss business. Much was made of the defendant’s general character, his or her demeanor in court, whether he or she looked suitably grief-stricken over the victim’s death, and so on. Sometimes the defense amounted to little more than the accused person saying, “I’m not guilty,” and sometimes the court whizzed through the entire trial in half an hour or so. Very frightening.

What was the hardest part of the book to write?

The structure. My original plan to use James Marsh’s story as the central narrative proved impossible [to execute]. There just wasn’t enough known about him. His background was too humble and his work not well-enough known for him to have left much of a trace. However, when I looked into the court case that had prompted him to develop his test, I found the most extraordinary murder mystery. All the accounts of the Marsh test that I’d read just dealt with this in a couple of sentences.