Indrajit Dutta, 50, an engineer and his wife Jasmine Patel, 45, a doctor and their daughter Oshin, took the extreme step, a couple of days ago, a senior police official said.
The incident, however, came to light this morning after their maid returned to work, he said.
The maid rang the door bell several times, but when there was no response, she opened the door with a spare key.
Upon entering the flat, she found Indrajit's body hanging from the ceiling fan in the living room, the officer said.
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Indrajit was in an inebriated condition. When he saw the bodies of his wife and daughter hanging, he took them down, came to the living area and committed suicide, the officer added.
The police found two suicide notes from the spot, purportedly written by Indrajit and Jasmine.
The suicide note purportedly penned by Jasmine said she had been ailing for long and had had lost interest in life, Navi Mumbai Police Commissioner Hemant Nagrale said.
In the suicide note, the woman expressed her desire to donate her body as well as that of her daughter to the KEM hospital, he added.
As per the suicide note, purportedly written by Indrajit, he found the bodies of his wife and daughter hanging and hence lost desire to live, the officer said, adding a probe is on.