NEW DELHI, Oct. 27 -- A 21-year-old woman, along with her ex-boyfriend, allegedly killed her live-in partner in Timarpur's Gandhi Vihar and tried to stage it as a fire incident using her knowledge of forensic methods, police said on Sunday, adding that it was revenge for taking obscene videos of her. The woman, her ex-boyfriend and another man have been arrested. Around 2.50am on October 6, police said, a fire was reported at the fourth floor Gandhi Vihar room of the victim, a 32-year-old UPSC aspirant. Once the blaze was doused, a severely burnt body was found. The police had initially registered a case under provisions related to negligent conduct with fire, pending post-mortem and forensic analysis. However, investigators soon grew suspicious after the victim's cousin raised doubts about the nature of the death. CCTV footage from the area showed two people entering the building before the fire and one woman leaving shortly before it broke out. Police identified her as the victim's live-in-partner, a 21-year-old BSc forensic science student from Moradabad, Uttar Pradesh, who had been in a relationship with the victim since May this year. According to the police, the victim and the woman had met in May this year and had been living together. During the relationship, the victim allegedly recorded obscene videos of the woman and stored them on a hard disk. "When she discovered the videos and asked him to delete them, he refused and even made up false stories to humiliate her," said a senior police officer. "Feeling trapped and angry, she confided in her ex-boyfriend who decided to take revenge." Investigators said the woman, her ex-boyfriend and another associate, then conspired to kill the victim and make it look like a fire accident. The woman, who had a keen interest in crime shows, allegedly used her knowledge of forensic methods to plan the cover-up, a senior police officer said. On the night of October 5, the trio visited the victim's flat, where they allegedly strangled and beat him to death before pouring oil and alcohol over the body. The ex-boyfriend, who works as an LPG gas distributor in Moradabad, then set up the scene for a fire. "He knew how to manipulate the cylinder. They opened the regulator and ignited the fire using a lighter, leaving the cylinder near the victim's head," the officer said. "About an hour later, the cylinder exploded, and the body was charred." The accused were traced using CCTV footage, call detail records, and technical surveillance. After multiple raids, the woman was arrested on October 18 from Moradabad....