On Sunday morning, a neighbour, who used to purchase milk from their shop everyday at 6 a.m., found it closed.
The victims belonged to the same family and majority had lived in the same home in Burari village in the northern part of New Delhi, said police officer Vineet Kumar.
They ran two shops on the ground floor of the three-storey building.
In a major twist of events in Burari case, the culprit is believed to be one of the deceased family members, claimed reports while denying any instance of forceful entry in the house.
"We don't know the reason yet, our team is at the spot and investigating this", said a police official posted in the area, who did not give further details.
"During search of the house, certain handwritten notes have been found which point towards observance of some definite spiritual, mystical practices by the whole family", the statement said. Another police officer said that suicide is being suspected but possible angles of homicide are also being investigated. A 77-year-old woman was the only one found lying on the floor. She had lived in the two-storey house with two sons, Bhavnesh (50) and Lalit (45), and one daughter, Pratibha (57), for almost 25 years, a local said. The family was into plywood business and they were staying in the locality for the last 20 years, the locals said.
The newspaper said that at around 8 a.m. Sunday, a neighbour with whom the businessman used to go for morning walks went to see him and found the door of the house open and the 10 people, including the businessman, hanging.
The police said that they were probing all angles and have not ruled out the possibility of foul play in the incident. Then the neighbour called the police. "What I saw there left me shocked", said Gurcharan Singh, another neighbour.
"No father can kill his own son ... how would a mother be able to kill her own children?"
According to media reports, the family migrated to the capital from the northwestern state of Rajasthan about two decades ago and police were trying to get in touch with relatives there.
Some locals said CCTV cameras in the area could have helped solve the murder.
Police are investigating to establish its links with the deaths.