A 25-year-old  UPSC aspirant named Benzi Singh from Manipur suffering from severe insomnia and depression, allegedly stabbed a 65-year-old security guard named Ram Bahadur Khatri to death in south Delhi's Safdarjung on Wednesday.

Khatri who manned the B/6 block in south Delhi's Safdarjung Enclave was stabbed in the neck by Benzi while he was asleep inside an autorickshaw.

The police said that Benzi was angry with a autorickshaw driver in his area after he had a fight with him last week. Singh mistook the security guard for a driver and killed him, added the Police.

Deputy commissioner of police (south), Vijay Kumar said, "Few weeks ago, Singh had an altercation with an autorickshaw driver over the fare. Since then, he harboured a grudge against them and wanted revenge. On Wednesday, around 2.30am, he saw Khatri sleeping in the auto rickshaw and mistook him as one of the auto drivers from the neighbourhood. He allegedly took out a paper cutter and stabbed the guard to death."