The Delhi Police has accessed the call detail records of the 11 members of a Burari-based family who were found dead under mysterious circumstances on Sunday.
Those who spoke to the 11 family members on the phone would be asked to appear for questioning, officials said.
Over 100 people, including the other family members and neighbours, have been questioned so far in connection with the deaths.
The police are scanning the call detail records of the 11 family members.
The focus is on the call detail records of the last four-five months. It was around this time that the notes, confiscated by the police from their house, make a mention of "badh tapasya" or Banyan tree puja rituals that the family replicated on the intervening night of Saturday and Sunday.
"On the basis of these records, a list of more than 500 people to be questioned has been prepared and different teams will question them," the officer said.
Ten of the 11 members of the family were found hanging from an iron-mesh in the ceiling on Sunday, while the body of 77-year-old Narayan Devi, the head of the family, was lying on the floor in another room of the house.
Her daughter Pratibha, 57, and two sons Bhavnesh, 50, and Lalit, 45, were among the deceased.
Bhavnesh's wife Savita, 48, and their three children - Maneka, 23, Neetu, 25, and Dhirendra,15, were also found dead.
The others who were found hanging were Lalit's wife Tina, 42, their 15-year-old son Dushyant and Pratibha's daughter Priyanka, who was engaged last month and was supposed to get married by year-end.
On Wednesday, the police had recovered CCTV footage that showed some members bringing stools and wires that were used for their hanging. They had also found 11 diaries which had "psychological musings" and things about attaining "road to God".