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Detectives are always looking for ways to use new areas of forensic science to solve crimes. In Hull, investigators who are trying to solve the murder case of a teenage boy found strangled and submerged in a river turn to forensic ecologist Rosie Everett. Using her expertise in single-celled organisms called diatoms, which are so tiny they are invisible to the naked eye, she soon proves that traces of algae found on the suspects’ shoes are a match for samples taken from the crime scene. Rosie’s evidence is key to the prosecution’s case, and for the first time in a murder investigation, evidence from this very specialised area of forensic science helps deliver justice for the victim and the victim's family.

Our second case in this episode investigates the chilling murder of Lakhvinder Cheema, who was fatally poisoned in his Southall home while sharing a curry with his fiancée Gurjeet Choongh.

In January 2009, Cheema’s spurned ex-lover, Lakhvir Singh, enters his home and secretly spikes their dinner with a rare lethal toxin, Indian aconite. Hours later, he dies in hospital and Gurjeet is left fighting for her life. The horrific poisoning – the first such case in England since 1882 – leads police to expert witness Professor Monique Simmonds, who is based at the Royal Botanic Gardens in Kew. A renowned plant chemistry expert, Professor Simmonds analyses samples of leftover curry, the victim's blood and suspicious herbs found in Singh's coat pocket, and finds a crucial link between them. With Monique providing investigators with enough evidence to prosecute Singh, she is convicted of murder and sentenced to 23 years in prison. Featuring interviews with Professor Monique Simmonds, leading barrister Edward Brown KC and forensic psychologist Dr Soham Das, this episode unpacks the remarkable details of a rare and haunting case.