A 54-year-old man allegedly stabbed three neighbours to death at a residential building in south Mumbai on Friday, police said.
Two others were injured in the attack and the condition of one of them was serious, they said.
Earlier, a senior police official had put the death toll at four.
The grisly incident took place around 3.30 pm at Parvati Mansion on Grant Road, an official said, adding that the accused, identified as Chetan Gala, was soon arrested.
His wife and children had left him two months ago, and he suspected that his neighbours had instigated them, the official said.
He had been mentally disturbed ever since, and on Friday, upon spotting his neighbours, he went to his house, picked up a knife and allegedly attacked five persons from neighbouring families.
The injured were rushed to a private hospital in Girgaum and civic-run Nair hospital where Jayendra Mistry (77), his wife Ilaben Mistry (70) and Jenil Brahmbhatt (18) died during treatment, the official said.
Prakash Waghmare (53), a house help, and Snehal Brahmbhatt (44) were undergoing treatment. The condition of Snehal Brahmbhatt was said to be critical.
After the incident, the accused locked himself inside a room in the building.
He refused to come out when the police reached the spot, but relented when they threatened to "break the door and hit" him, said the official.
Police took him into custody and also recovered the knife used in the attack.
He allegedly admitted to the crime while telling the officials that he was disturbed after his family members abandoned him.
Though visibly mentally disturbed, he was not undergoing any medical treatment, the official said.
A First Information Report (FIR) under sections 302 (murder) and 307 (attempt to murder) of the Indian Penal Code was registered at D B Marg police station and probe is underway, the official added.
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