A 36-year-old security guard and his wife allegedly murdered their three-year-old son before consuming poison at their house in Hoskote near here on Thursday.
Their five-year-old daughter, however, left the house when the couple tried to force feed her poison.
The incident came to light when neighbours noticed the girl standing a little away from the house and crying inconsolably.
When there was no response from inside the house, the neighbours entered the house and found the boy lying in a pool of blood and the couple lying dead next to each other.
The dead were identified as Shivraj Joshi, Usha Joshi and Nikhil.
The Hoskote police rushed to the spot and found some empty bottles of poison.
The police also found a note in Hindi, stating that “no one is responsible for their death”.
According to the police, Joshi hailed from Nepal and was working as a security guard in a private firm for the past nine years. The neighbours told the police that Joshi was unwell and had stopped going to work. The couple had had a fight on Wednesday night.
“We suspect that a domestic feud might be the reason, but investigation is on,” an official of the Soolibele police said.