A 31-year-old contractual bus driver of the Delhi Transport Corporation (DTC) allegedly hanged himself after killing his wife and two sons at their residence in Naharpur village of north Rohini area, police said on Thursday.
Dheeraj Yadav was found hanging from a ceiling fan, and the bodies of his wife, Aarti (28), and sons, Hiten (6) and Atharav (3), bore stab injuries, they said.
The police said Mr Yadav has left behind a suicide note, and an investigation is underway to ascertain the motive behind the killings.
The couple and their two children lived in a joint family. They resided on the second floor of the house, while his parents lived on the ground floor and his elder brother and his family lived on the first floor.
According to the police, Yadav's father, Maha Singh, spotted his body hanging from the ceiling fan through a window on Thursday morning and informed them.
Legal action has been initiated, and further investigation is in progress, said Pranav Tayal, Deputy Commissioner of Police (Rohini).
A kitchen knife apparently used to stab the woman and the kids was recovered from the spot, the police said, adding that the bodies will be handed over to the family after post-mortem.