Raju, a property dealer in the area, was allegedly shot at by the duo -- identified as Vinod and Yakub -- yesterday when he was standing at his under-construction house in Sangam Vihar.
A property dispute is believed to have been the reason behind the attack, police said.
On hearing Raju's cries for help, locals gathered and gheraoed Vinod and Yakub, who tried to flee from the scene, they said.
The locals beat the duo with sticks and bricks, officials said, adding, Vinod died on the spot in the incident.
According to police, Vinod was wanted in about 50 cases of murder and dacoity in Delhi and Uttar Pradesh.
Raju and Yakub were rushed to a hospital, where the condition of the latter was stated to be critical.
Police lodged cases of murder and attempt to murder against the mob and Yakub respectively.