A trainee engineer in a mobile manufacturing company, Ms Ratour shared a third-floor apartment in the Shatabdi Rail Vihar Apartment Society with five friends.
On Wednesday morning, not long before she was shot, she had gone down after a phone call.
"Initial investigations suggest that she got a call from a man believed to be her boyfriend Ashwani at around 6.05 a.m. She later went to meet him in the parking area of the building," Mr Singh said. She had reportedly been avoiding Ashwani's phone calls for several weeks.
Ms Ratour's family in Yamuna Nagar in Haryana have also told the police about him.
The shooter has not been identified yet as the CCTV at the main entrance of the complex was not working, the police say.
"We could not identify the accused person due to unclear image of his face. The call details records of the deceased are being examined," said Mr Singh.
Ms Rathour started working last year after completing an IT course from a college in Punjab. That is where she met Ashwani, who is from Etawah in Uttar Pradesh.
The police have formed three teams to investigate the case and are questioning security guards of the society and her office colleagues.
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