Felon vs Flora: How To Catch a Killer with a Plant
Writer: Clara Wilkinson
Editor: Nirvan Marathe
Artist: Amaranta Chavez
If I told you that you could catch a killer with a plant, you would probably laugh in disbelief. Yet forensic botany does exactly this. Analysis of plants can provide vital evidence in police investigations, from linking a suspect to a crime scene to finding where a body is buried.
Some of the most powerful poisons in the world are found in plants. In 2009, Lakhvinder Cheema was poisoned by his ex-lover. Plant forensic experts at Kew analysed samples from the victim’s stomach and identified the poison as a deadly toxin from Aconitum ferox. This deadly plant is native to the Himalayas. Knowing this, the police uncovered that the murderer had planned the murder, travelling to India beforehand to obtain the poison. This evidence was used in court to convict the murderer of a pre-meditated attack. She was given a life sentence.
Plants don’t need to be directly involved in a crime for forensic botany to be useful. All self-respecting criminals know not to leave DNA at a crime scene, but few would think to worry about pollen. Although hay fever sufferers might disagree, pollen is generally thought to be a harmless powdery substance ferried from flower to flower by bees in summer gardens; however, pollen can cling to clothes and corpses, and bring murderers to justice. Don’t believe me? Let’s look at the murder of Mellory Manning in 2008 in New Zealand. Police suspected the notorious Mongrel Mob gang but had no evidence that the murder took place in their territory. When traditional forensics was unable to pinpoint the murder location, the pollen expert Dallas Mildenhall was called in to help following the discovery of residual pollen on the victim’s body. For months, this pollen was studied and eventually he noticed a discrepancy: one of the pollen grains was mutated. This was then matched to mutated pollen found in large amounts near the gang’s headquarters. This evidence was enough to scare a gang member into revealing everything and the murderer received a life sentence. The gang may have thought about CCTV and cleaning up DNA from the crime scene, but little did they suspect that their downfall would be a few grains of mutated pollen.
You might be thinking that this is just standard forensics with a botanical twist. The story of forensic botany, however, extends further.
A key part of any murder investigation is finding the body. When a human body decays, around 2.6kg of nitrogen-containing compounds are released into the soil. Although this is a rather grisly image, the result is actually a surge in chlorophyll levels and a resulting bright patch of green vegetation near the rotting body. This might seem to be a crude method, yet studying plants above dead bodies can give surprisingly detailed results. For instance, if the missing person was known to be a heavy smoker, the leaves of plants above their body will be highly discoloured. This is because of the high levels of cadmium in the smoker’s body leaking into the surrounding soil. Cadmium disrupts the molecular machinery of photosynthesis, severely impacting the wavelengths of light that can be absorbed, thus changing leaf colour. Although less useful in cities, this approach would be invaluable in the search for bodies in large natural areas, such as forests.
In the battle against felons, plants might be our greatest weapon. A knowledge of plants can help identify poisons, link suspects to a crime scene, or find buried bodies. A criminal may use increasingly sophisticated methods to evade DNA forensics. A murderer may choose a location far from CCTV or prying eyes to bury their victim. However, forensic botany has the power to trump both of these. Although we can’t abandon all other police work and rely on plants entirely, when we are struggling to find clues, plants can provide some vital evidence. So, the next time you start to dismiss botany as boring, remember how a single grain of pollen can catch a killer.