The accused was later arrested from central Delhi's Kamla Market during picket checking at GB Road, they said.
The victim, Yahiya Khan, was good friends with one Udayan, a builder.
Khan owned a clothes shop in Chitli Qabar. He did not approve of Udayan's closeness with his wife and their relations had soured because of this issue, the police said.
In order to resolve their issues, their family members decided to hold a meeting between them at the sweets shop.
However, Udayan snatched the pistol from Khan and shot him, they said, adding he then escaped from the spot.
Later, police arrested him in Kamla Market.