A jilted Indian man’s fury over being rejected by his former girlfriend led him to stab then hit the helpless teenager to death with a slab of concrete, initial police investigations revealed, as the bystander effect played out on a bustling Delhi street.

Police arrested the 20-year-old man in Uttar Pradesh on Monday, a day after he attacked and killed the girl, 16, in the Rohini neighbourhood in capital New Delhi.

Identified by the authorities as Sahil, the refrigerator technician had fled by bus to the neighbouring north Indian state after his brutal bludgeoning on Sunday evening.

His location was traced to the city of Bulandshahr, more than 130km away from the Shahbad Dairy crime scene, after he made a phone call to his father, allowing police to nab him.

The girl, Sakshi, had been on her way to a birthday party when Sahil intercepted her, local police said.

He can be seen in closed-circuit television camera footage repeatedly stabbing her with a knife while pinning her to the wall with another hand, at one stage stopping to adjust his grip on his weapon after it got stuck in her skull, before hitting her head with a cement slab that was lying close by.

An initial post-mortem showed her skull was ruptured by a blunt object and that she was stabbed 16 times, the police said, while the final autopsy report has yet to be released.

The police have described the murder as a crime of passion, with the two having been in a romantic relationship since 2021.

Sahil was infuriated by Sakshi’s decision to end their relationship and had threatened to kill her a few days ago, a police officer told local media, adding that Sahil harboured suspicions she was talking to a former boyfriend.

Investigators are also looking into a tattoo of the name “Praveen” on her hand.

The last post on Sahil’s Instagram account, which is public, dated April 14 shows him smoking shisha with his friends while rap music played in the background. The social media platform’s users left comments on his page admonishing him for his alleged murder.

Bystander effect on notorious street

In camera footage of the attack, at least 10 people can be seen walking past them on the street in the Shahbad Dairy district in north-western Delhi.

Some stopped to watch without intervening or calling the authorities, seemingly afflicted by the bystander effect, the social psychological theory that individuals are less likely to offer help, with responsibility diffused when other people are present.

Local residents speaking to Indian media said they were afraid of getting involved for fear of being attacked themselves.

“This neighbourhood, and particularly this street, is notorious for drug abusers. People drink openly, and if anyone questions them, they abuse and attack them,” said Mr Indra Dev, whose son was questioned by police as part of investigations after he was captured in camera footage on the street.

“Few would want to risk their lives in a place where such attacks are so common.”

The police were alerted to the incident by a police informer at around 9.35pm local time on Sunday, a Delhi police officer said, a considerable delay after the crime was recorded at 8.45pm according to CCTV time stamps.

“If we notice such incidents, we must intervene to the best of our ability and dissuade an assailant from committing such crimes,” Delhi’s top cop Deependra Pathak told India Today.

“Such interventions would contain a crime and save a life,” he said, adding that Sahil faces the death penalty for the brutal murder.

Former Uttar Pradesh police officer Vikram Singh said it was an “avoidable” death.

“People could simply have shouted to frighten Sahil, or hurled bricks at him to dissuade him. With 12 to 13 people standing there, it was very possible to save her,” he told The Hindustan Times.

The murder recalled other gruesome killings in India’s capital.

In November 2022, a chef and food blogger was discovered to have killed and chopped up his live-in partner’s body into at least 35 pieces before dumping them in the forest.