The shooting took place at around 1:30 am in Lucknow's Gomti Nagar extension area when Vivek Tiwari was driving with a former colleague. Two policemen on patrol flagged his car, asking them to stop. Mr Tiwari first hit the police patrol bike and then rammed a wall while allegedly trying to escape, the police said.

Constable Prashant Chowdhary opened fire at the car on noticing "suspicious activity" and the bullet pierced through the windscreen, Lucknow police chief Kalanidhi Naithani said.

Vivek Tiwari died of bullet injury at a hospital in the city, the police said. "The post-mortem report establishes a firearm injury from a bullet on the left side of the chin. The viscera of the victim has been preserved," Anand Kumar, Uttar Pradesh Additional Director General of Police (Law and Order) said.

The autopsy revealed on Saturday that the bullet hit Tiwari's chin and got stuck between the neck and the head, leading to his death due to excessive bleeding.

Police investigating the case said the constables used "excessive force". Uttar Pradesh Police chief OP Singh released an unusually strong statement seeking "forgiveness". "We are determined to punish and wean out such rogues in uniform who hang our heads in shame," he said.

Constable Prashant Chowdhary said he opened fire in self-defence. "The lights were off. When we reached the car, whoever was inside it started the car. We parked our bike in front of the car. He hit our bike. I waved at him to stop but he reversed the car and hit us again. We asked him to come out. But he reversed for the third time and hit our bike with full force. I fell and then got up. I drew my pistol to scare him. When he tried to run over me, I had to shoot in self-defence," he said.

Mr Tiwari's co-passenger who filed a complaint later, however, has a different version. "The police just waylaid us and tried to stop us forcefully. Sir (Vivek Tiwari) didn't stop the car. We didn't realise who they were. There was no accident. We were trying to leave from the side. We hit the bike but they had already gotten off the bike. One of them had a lathi. The man in the front just pulled out a revolver and fired," she said.

Uttar Pradesh Chief Minister Yogi Adityanath said he will ask for a CBI investigation if needed. "It was not an encounter. An investigation will be conducted in this incident. If needed, we will order a CBI inquiry into the incident," he said.

Vivek Tiwari had spoken with his wife minutes before he was shot at. "Is it a crime not to stop a car? I want to ask the chief minister, what kind of law and order is this?" Mr Tiwari's wife Kalpana told reporters. "We've three demands -- an SIT to be formed, job for my brother's wife and right amount of compensation. We are also waiting for Yogi ji to come here, else we'll take Vivek's body to his residence," said Vivek Tiwari's brother.