Police has also recovered a pistol which was allegedly snatched from the slain constable by the accused before fleeing.
"The four robbers including two minors were planning for a robbery when they were confronted by the policemen who were patrolling the area.
"The cops tried to take them to the nearby police station when the accused opened fire killing constable Jagbir Singh and critically injuring constable Narendra. All four accused have been nabbed in the case," a senior police official said.
The incident had taken place around 1:30 AM yesterday just a few hundred metres from Vijay Vihar Police Station during which Singh died on the spot while his colleague Narendra (42) was injured.
Jagbir had served in the Indian Army for 15 years and had joined Delhi Police in 2008.