Those who were found hanging had their mouth taped and their faces covered with cloth pieces cut from a single bedsheet. The woman found dead on the floor was without a blindfold and had been allegedly strangulated.
The hands and feet of the children were tied, the police said, adding that stools were found overturned at the spot.
The police found handwritten notes which indicated a "religious or spiritual angle" to the deaths. A police officer said a probe will be conducted to find "if the family indulged in occult practices" or they followed "any godman".
"We have found handwritten notes detailing how hands and legs are to be tied and the manner in which the bodies of the 10 persons were found reflected what was written in the notes. They are exhaustive notes and we are studying them," Joint Commissioner of Police (Crime) Alok Kumar said.
Another officer said the notes were found in registers. "They talk about how a person can overcome fear by covering eyes and mouth, how a person can attain salvation, and how the human body is temporary but the soul continues to live on," he said.
"The notes talk about if a group of 11 people follows these rituals, all problems would ease out and they would attain salvation. Some notes have dates on which they were written while others don't. All the notes talk about reaching the end and gaining peace," one of the investigators said.
While a murder case has been registered, the police suspect the deaths to be a case of a suicide pact.
"It is possible that the elderly woman was strangulated since she was not in a condition to climb a stool. We are probing whether the children were killed or were convinced to take the extreme step," one of the officers privy to the probe said.
According to the police, they were informed by a neighbour that six to seven people have committed suicide. On reaching the spot, they found 11 people were dead.
The deceased were identified as Narayan Devi, who was found dead on the floor, her daughter Pratibha (57), her two sons Bhavnesh (50) and Lalit Bhatia (45).
Bhavnesh's wife Savita (48) and their three children - Meenu (23), Nidhi (25) and Dhruv (15).
Lalit Bhatia's wife Tina (42) and their 15-year-old son Shivam were also among those found dead.
Pratibha's daughter Priyanka (33), who was engaged last month and would have married by the end of this year, was also found hanging.
Bhavnesh ran a grocery store on the ground floor of the house. He used to open his shop around 6 am, the family's neighbour Amrik Singh said.
"Today, the shop was not opened till 7 am. The milk van had arrived outside the shop. A couple of neighbours had gathered because the van driver was continuously honking," Amrik Singh's father Gurcharan Singh, who claimed to be the first person to have seen the bodies, said.
"Then, I opened the main gate and went upstairs. What I saw there left me shocked," he said, adding that one could enter the house as the main door was not locked from inside.
Another area resident said, "They were all hanging with 'chunnis' while Lalit had a telephone wire wrapped around his neck along with a 'chunni'."
After that, the residents called the police.
A senior police official said the crime branch will investigate the case from all angles. The police have not ruled out the possibility of a foul play.
Chief Minister Arvind Kejriwal and Delhi BJP chief Manoj Tiwari visited the Burari colony where the incident took place.
The family was also into plywood business. They were living in the locality for more than 20 years, residents said.
They said they were in a state of shock after hearing what had happened.
Members of the family, who had come from places outside Delhi, alleged that the 11 members were killed.
Narayan Devi had three sons and two daughters. The eldest son Dinesh Bhatia lives in Kota, Rajasthan. Pratibha, who was younger to Dinesh but elder to Bhavnesh and and her other siblings, was a widow and was living with her brothers.
One of Narayan Devi's daughters, Sujata, lives in Panipat with her family.
"I can't believe that they committed suicide. Everyone was so happy. Someone has killed my family and the police have to find them," a sobbing Sujata said.
The post-mortem examination of the bodies is being carried out, the police said, adding that the report will give a clue about whether one of the family members killed the rest and then committed suicide or if the deaths were a result of a suicide pact.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)