Ombir Singh, a police official investigating the matter, said that all three sisters seemed to be mentally unstable.
Dolly, 43, Poonam, 41, and Neeru, 30 who lived in House No. 331 in south Delhi's Kalkaji area, had shut themselves in their home and had gone without food for two weeks - till the neighbours called police complaining of foul smell.
The stink was from the decomposing body of the youngest sister.
"We are yet to receive the post mortem report for Neeru, whose body was sent to the All India Institute of Medical Sciences (AIIMS)," said the police official.
"Poonam, the sole breadwinner of the family who was working as a lecturer in a polytechnic institute in south Delhi, said that she lost her job about six months back because of her repeated illnesses. Since then they have been living off the little savings that they had," Singh told IANS.
Dolly and Poonam have been admitted to the Sukhda nursing home in south Delhi by members of the Residents Welfare Association (RWA) of their locality.
"Their condition is better than before. Neeru's body has been taken to the crematorium by their cousin, who used to stay next door but nevertheless had no idea about the sisters' condition since they had shut themselves away from the outside world," Singh said.
Psychiatrist Sandeep Vohra said that the sisters were suffering from a serious mental disorder. "I haven't had a close interaction with them, hence I can't give the exact details but from what I have observed, all these women were mentally disturbed, severely," he said.
According to Vohra, the condition led them to be suspicious about any food item brought from outside, thinking it would poison them. "Hence the hunger and the starvation," he said.
He added that an incident like this shows that the government needs to address mental illness with utmost importance and people need to be sensitised about it as well.