Head constable Ramkishan, a resident of Nangloi, was shot dead in Kanjhawla on November 26 allegedly by four persons in a car who fled the scene.
"Commissioner Neeraj Kumar has announced a cash reward of Rs one lakh to persons providing information regarding those involved in the incident," a senior police official said.
Ramkishan (49) had managed to snatch one pistol from the attackers but they fired at him with another pistol, a senior police official said.
"A police team was conducting picket checking at the border. Ramkishan had stopped the car for checking. There were four persons inside the car.
"After frisking the two passengers in the rear seat, when he moved towards the driver side, the person sitting next to the driver fired at him," the official said.
The head constable was rushed to Braham Shakti Hospital where he was declared brought dead, the official said, adding that the four men escaped from the spot.
Ramkishan is survived by wife and two sons.