Rajesh (40) attacked his relatives with grindstones and stick when they were sleeping in their house in Nand Nagri yesterday night.
The deceased were -- Ram Kishan (60), his son Raju (26) and son-in-law Kiranpal (30). The injured were Ram Kishan's another son-in-law Tarun (28) and grandson Karan.
"Accused Rajesh also sustained injuries in head and leg as he tried to escape from the house after bludgeoning his relatives. He is now undergoing treatment at a hospital. He is under police custody and a case of murder has been registered against him," said A K Singla, DCP (north-east).
The accused, along with his son Aditya, came from Alwar to his in-laws' place after a dispute with his wife on Monday morning. Later, his wife Rakhi too came, along with their other children.
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The family was trying to resolve the dispute and Kiranpal, who lived in the neighbourhood, joined in the effort.
In evening, Rajesh convinced Kiranpal to stay back so that his problem could be solved through his mediation.
Police suspected that some sedative might have been mixed with the food eaten by the family in the dinner as the accused went on a killing spree without drawing attention from any of the family members.
Later, the accused tried to escape by jumping from second floor of the house to an adjacent building and then down to the lane but he sustained injuries in head and leg. He was caught by neighbours.
Amid a ruckus, the rest of the family members discovered the injured and rushed them to a hospital where Ram Kishan, Raju and Kiranpal were declared dead on arrival by the doctors.