A couple and their 16-year-old daughter were found murdered with stab wounds in their house here early on Wednesday, police said. Their son was found injured.
Mithilesh and Siya, a couple in their 40s, and their daughter Neha were found dead in south Delhi's Vasant Kunj area.
The neighbours entered their house to check on them after finding the main door ajar at around 4.30 a.m. and informed the police, Joint Commissioner of Police Ajay Choudhary said.
The neighbours told the police that they heard the son, Suraj, 19, crying for help from the balcony of their apartment on the first floor.
"He was heard shouting that his mother had saved him," the officer said, adding that his statement was being recorded.
Choudhary said a kitchen knife was used to cut the fingers of the deceased.
Police have formed eight teams to probe the case. "We are investigating from all possible angles," he added.
Pinki, a relative of the family, told IANS that Suraj was kidnapped and later rescued about three years ago.
She suspected the murders to be the handiwork of "outsiders".
(With inputs from agencies.)