The IIT PhD scholar, who allegedly murdered a teenaged girl from Manipur in New Delhi, is a "pervert and maniac" who suffers from obsessive compulsive disorder, police said on Monday.

Pushpam Kumar Sinha (34), who is doing research in wave mechanics from IIT-Delhi, was arrested on Sunday for allegedly strangling Ramchanphy Hongray (19) at her second floor accommodation in south Delhi's Munirka on Saturday.

Sinha allegedly strangled the teenager after she "angrily resisted" his advances. "He felt that she might inform police and so he strangled her for three minutes. To make it as a case of accident, he put her face on the gas stove and lit it.

"Initially there was no suspicion of foul play in the incident but the post mortem report suggested that she died of strangulation and not due to burns. We zeroed in on Sinha after discreet enquiries," Deputy Commissioner of Police (South) H G S Dhaliwal told reporters.

Dhaliwal said that during searches at Sinha's room, which is one-floor below the girl's accommodation, it came to light that he was suffering from obsessive compulsive disorder.

"Grafittis on the walls showed that he was a pervert and maniac. He had a complex. He wrote in his diary that he was not able to make friends with girls. One of the graffiti read that 'this is the time to make girl friend. I am finally making someone," he said.

"A very vulgar kind of red graffiti was found on the wall of his room and he wrote many things," Dhaliwal said, adding it took around four hours of interrogation to make him confess to the crime.

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