The notes - which talk of unusual religious beliefs - provide a motive in the case, say the police, who initially thought it was mass suicide and then said it could be mass murder by one of the family, who then committed suicide.
"Coincidentally, these notes have strong similarity with the manner in which the mouths, eyes etc. of the deceased were tied and taped", it added. His family had lived in the home for more than two decades. "The last, a 75-year-old female, was dead on the floor", a Delhi police official said, Deutsche Welle reported. Then the neighbour called the police. "When we reached the shop in the morning usually it is open and running early around seven, but today they were not, which is very unusual as they are very particular about timings. I couldn't bear watching anymore", he said.
The police was investigating the case and questioning neighbours and relatives of the family.
"No father can kill his own son". They arrived at the scene to find 11 members of the family dead at their residence in Gali number 4.
Calling it a mass murder, a media report said that it was an insider's job, who was under some tantrik's influence.
The incident has caught the attention of the capital, and chief minister Arvind Kejriwal, Delhi BJP chief Manoj Tiwari, and Congress leader J.P. Aggarwal visited the area to express their condolences.
'In a video posted on Twitter by Kejriwal's ruling party, the neighbors are heard telling Kejriwal that the family was busy with wedding preparations.
A neighbour of the family said they couldn't have committed suicide, New Delhi Television reported. On Sunday morning, a neighbour, who used to purchase milk from their shop everyday at 6 a.m., found it closed.
Police are investigating to establish its links with the deaths.
Indian TV channels broadcast interviews with neighbors who said the family did not have any discord among themselves.
"The initial investigation, the way their hands were tied and mouths gagged, led us to register a case of murder".
Police official Rajesh Khurana told reporters that all angles were being investigated.