The Myth Of Untraceable Poison

The news of the apparent poisoning of Sergei Skripal and his daughter Yulia produced a lot of speculation over what might have made two people very ill so suddenly. All sorts of wild theories can emerge in situations like this where so little information is known for certain. Identifying poisonous substances is vital, particularly when people become ill from their effects and need medical treatment. If the cause of the problems is known, better remedies can be given instead of symptoms being treated as they present themselves. With more knowledge, the poisoned individuals are more likely to survive. From a legal point of view, it is important to identify a poison if it has been deliberately administered so evidence can be obtained for any potential criminal prosecution.

It has now emerged that it was a nerve agent that was used against Skripal – but this still leaves some possibilities, as there are several types of nerve agent. That this information should emerge three days after the poisoning is unsurprising. Tests take time, and the police will want to be certain of their facts without giving away information that could compromise an investigation. Since Skripal’s collapse, there has been plenty of speculation, including talk of secret untraceable poisons. The idea of being able to kill without being detected is terrifying, but there is no such thing as an undetectable poison. Toxins can be incredibly difficult to detect, and the circumstances around death from poisoning, such as the decay of the body, can mean the evidence is lost. But there is no such thing as a substance that can’t be traced. The idea of untraceable poisons is nothing new. It is a popular trope of crime novels and spy movies as it is an easy way to bump off a character. If there is nothing to trace, the culprit can get away with it without leaving inconvenient and incriminating evidence that can bog down the plot with tedious scientific explanations. In real life, things are different. If poisoning is suspected, considerable effort will be made to identify the poison used, though it isn’t always easy.

Before 1840 there was no reliable way of extracting and identifying poisons from a body. When some cases appeared in court where poison was strongly suspected but couldn’t be proven, scientists made concerted efforts to establish methods of extraction and detection. Forensic toxicology emerged as a consequence of Victorians trying to bump each other off with poisonous substances. As analytical chemistry has advanced over the years, the range of poisons that can be detected has grown, and the amount of a substance that is needed for correct identification has decreased. More poisons can be detected in ever smaller amounts, making it less and less likely that poisoners will get away with it. (Unfortunately, that hasn’t stopped some from trying.)

One idea for an untraceable poison was put forward by Dorothy L Sayers in her novel Unnatural Death. A bubble of air injected into a vein between the toes would move to the heart, causing an air embolism that results in death. It seems like the perfect crime. The injection site would be difficult to find, and the substance would be impossible to identify as air would leave no trace. However, there are several problems with the idea – location and quantity. Air injected in the foot is likely to be absorbed naturally into the body long before it makes it to the heart. Or such a large volume of air would have to be injected to cause a lethal embolism that it would be physically very difficult, if not impossible, to do. The victim would probably notice what was going on and protest.

Another possibility for an untraceable poison, one that has been tried by real-life murderers, is an injection of a substance naturally found in the body or that is quickly broken down and eliminated, leaving nothing behind. The classic example of this is Kenneth Barlow, who injected his wife with a large dose of insulin, believing it would kill her and be indistinguishable from the insulin found naturally in the body.

The death of Elizabeth Barlow was certainly a puzzle for the pathologists investigating the case, but close examination of the body identified injection marks on the buttocks. The flesh around the injection site showed high levels of insulin. The problem for the poisoner is that once the body has ceased living, the processes that break down a substance often also stop, leaving an excess for the pathologist to find.

A third possibility is the use of a previously unknown substance. In such a case there may be no specific test available to toxicologists, but that doesn’t mean the substance can’t be identified. When Alexander Litvinenko was assassinated using polonium-210, his was the first case of such poisoning to be known. But because polonium-210 is such an unusual substance, its very presence became particularly suspect. Any traces of it could be a clue to the events around Litvinenko’s poisoning. It took time to identify the poison, but once it was known, a strong case could be put together against his poisoners.

The final possibility is that a substance is used that is so potent that tiny amounts could be fatal: where the quantity needed to kill is so small that finding it among kilograms of human tissue tests the limits of modern analytical detection. For example, ricin can be fatal in minute quantities; less than a milligram can kill if it is injected. Finding traces of poison no bigger than a grain of salt in a heavy cadaver is difficult but not impossible. It may be like searching for a needle in a haystack, but that needle is in there somewhere, and it can be distinguished from the hay if you know what you are looking for. The case of Georgi Markov on Waterloo Bridge in 1978 required a lot of time-consuming testing to confirm that it was ricin that was responsible for his death.

In the case of poisoning using an unknown substance, the first thing to do is narrow down the possibilities. Skripal and his daughter are currently being treated in hospital, and their condition will be under constant supervision, with numerous samples being taken regularly for analysis. Symptoms observable from CCTV and attending medical staff will help shorten the list of suspect nerve agents. Samples obtained from the possible site of their poisoning could offer more clues. However, tests are time-consuming and not always conclusive. Patience and careful investigation will be needed to offer the best hope for Skripal and his daughter.

Credit: Kathryn Harkup for The Guardian, 8 March 2018.