LUCKNOW, April 10 -- In a case bearing unsettling similarities to the slow-poisoning plotline of Bollywood thriller, 'Dhurandhar: The Revenge', an attempt to murder FIR has been registered against unknown individuals after a prominent businessman from Varanasi was allegedly administered thallium, a rare and highly dangerous slow-acting poison. Police said an FIR was lodged at Kotwali police station, Varanasi, on Wednesday night on the complaint of Khushboo Singh, wife of former Samajwadi Chhatra Sabha national general secretary Sandeep Singh, 41, after doctors at a Mumbai hospital reportedly confirmed traces of thallium in his blood. Sandeep Singh, who also runs two transport firms linked to road construction logistics, is currently undergoing treatment at his Lucknow residence under medical supervision, family members said. The case has triggered concern not only because of the victim's political and business profile, but also because thallium poisoning is rare, difficult to detect, and often initially resembles neurological disorders. Khushboo Singh alleged that an unknown person may have administered the poison with intent to kill. The family, she said, became suspicious only after Mumbai doctors informed them that blood tests had revealed traces of the rare toxin. Police registered a case under attempt-to-murder provisions of Section 109 (1) of the BNS and launched an investigation. Kotwali SHO Dayashankar Singh said investigators are examining food consumption history, travel records, hospital stay details, business rivalry and political angles. The case has raised questions over whether the suspected poison was administered during travel, hospital stay, business meetings, or through food consumed outside home - a line of inquiry police are expected to pursue closely. According to the FIR content, Sandeep Singh first fell ill in late February 2025 while in Gurugram, where he had accompanied an acquaintance undergoing treatment. What initially appeared to be fever, tingling in the legs, body pain and vomiting gradually progressed into a severe neurological condition. He was first admitted to Medanta Hospital, then shifted to Max Super Speciality Hospital, where doctors reportedly suspected Guillain-Barre syndrome (GBS). As his condition worsened, he was airlifted to PD Hinduja Hospital, Mumbai, where toxicology tests allegedly revealed thallium in his bloodstream. Medical literature describes thallium as the "poisoner's poison" because it is colourless, odourless and tasteless, making it extremely difficult to detect if mixed with food or drink. Adding a forensic perspective, Dr Richa Chaudhary, head of department, forensic medicine and toxicology at Dr Ram Manohar Lohia Institute of Medical Sciences in Lucknow, said the symptoms and severity depend largely on the dose of thallium sulphate or thallium acetate, compounds historically used in glass industries and rodenticides. "It varies according to the dose. Mild toxicity may present with nausea, vomiting and diarrhoea, while severe poisoning can lead to hematemesis, massive diarrhoea and even death due to respiratory failure," she said. Chaudhary said the toxin often follows a clinically recognisable timeline. "Peripheral neuropathy typically begins after two to three days, while alopecia usually develops after around 10 days," she said. She pointed to a classic diagnostic triad seen in thallium poisoning: Skin rashes - a maculopapular eruption often showing a butterfly distribution over the face, peripheral neuropathy and alopecia (hair loss), "This triad is highly suggestive in toxicology assessment," she added. Ajit Singh, brother of businessman Sandeep Singh, said the family first lodged a zero FIR at Mahim police station in Mumbai on March 30, 2025, soon after doctors suspected poisoning. He said the police subsequently transferred the complaint to UP Police because the alleged place of occurrence fell under its jurisdiction. However, he stated that the case file was sent back to Mumbai nearly five months later, resulting in a delay in formal registration and investigation. "The FIR was finally registered on Wednesday after the Mumbai police commissioner, on February 27, 2026, again raised the matter with UP Police officials regarding the transfer of the complaint and the progress of the probe," Ajit Singh said. He added that Sandeep Singh remains bedridden and is still undergoing treatment under medical supervision, while the family continues to await clarity on how the rare toxin entered his system. The slow progression of symptoms has drawn comparisons with 'Dhurandhar', where the underworld don modelled on India's most wanted fugitive Dawood Ibrahim is shown being slowly debilitated by poisoning allegedly orchestrated by the character Jameel Jamali. However, unlike the film's fictional poisoning device, toxicology experts said thallium is medically far more consistent with prolonged neurological decline, as it enters cells by mimicking potassium and progressively damages the nervous system....