The accident happened on the intervening night of June 23 and 24, they said.
On June 22, Harvinder Madan, 52, his wife Bharti, 50, Satya Ranjan, 50, a homeopathic doctor and their family friend, and another man Gurvinder Singh, 42, were returning to Delhi from Punjab's Firozpur, the police said.
When they reached Mongolpuri flyover, their car hit the truck that was parked on the downhill side of the flyover. The truck's parking lights were not on and the car driver could not see it in the night, they said.
The four injured people were taken to different hospitals. Harvinder, Bharti and Ranjan died on the way to the hospital, the police said. Singh is under treatment and his condition is said to be critical, the police said.
The police said that they have filed a case against the driver and efforts are being made to arrest him.
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