Gurugram, Oct. 6 -- A 75-year-old retired Delhi government teacher was allegedly strangled to death at her home in New Colony, Sector 7, on Sunday night after she raised an alarm on finding an intruder inside, police said. The 22-year-old suspect was arrested after a three-hour search, during which he was found hiding in a tree behind an adjoining house. The victim, Madhu Sharma, had lived alone for about two decades in a dilapidated single-storey house built on a 250-square-yard plot belonging to her parents. She had been living separately from her husband, who died in 2010. The couple had no children. Police said the suspect as Suraj Gupta, 22, hailed from Samastipur in Bihar and lived in Madanpuri. He worked as a daily wager in Gurugram. Police said Gupta, a suspected habitual substance user, allegedly told investigators that he had surveyed Sharma's house several times and noticed that it remained dark on most nights. A senior police officer said Gupta allegedly scaled the boundary wall intending to steal cash and valuables but found little inside. When Sharma confronted him, he allegedly threatened her with a hammer and demanded Rs.100. "When she raised an alarm, he strangled her," the officer said. Police said neighbour Ishit Nagpal saw Gupta enter the house around 9.10pm. About two minutes later, he heard Sharma scream and alerted neighbours and the police. Residents gathered outside, blocking the suspect's escape route. Police said Gupta scaled a wall, crossed a neighbouring terrace and hid in dense vegetation behind adjoining houses. Inspector Sanjeev Kumar, station house officer of New Colony police station, said Gupta was found after around three hours hiding in a tree, around 25 to 30 feet above the ground. Police said Sharma's house had no functioning electricity or water connection and parts of the roof had collapsed. He said Sharma had approached police around 20 days earlier with several complaints, following which police helped restore the supply temporarily. Police said Sharma received a regular pension and had around Rs.8 lakh in her bank account. Residents said the plot is worth around Rs.6.5 crore. An FIR was registered against Gupta under Section 103(1) (murder) of the BNS at New Colony police station....