The grisly murders occurred after Hasnin Anwar Warekar and his extended family gathered late on Saturday at a home north of India’s financial capital of Mumbai for a family function, police officers said.
“The attacker, Hasnin Anwar Warekar, hung himself after slitting the throats of all other family members including his parents,” Gajanan Laxman Kabdule, a police spokesman in Thane, some 32 kilometres (20 miles) from Mumbai, said.
The sole survivor of the attack — Warekar’s sister — was taken to hospital after neighbours heard her screaming for help after midnight and alerted police.
Neighbours were forced to open a window to rescue the woman after the assailant allegedly locked all escape routes from the house before carrying out the attacks, according to local media reports.
“We still haven’t been able to speak with the attacker’s 21-year-old sister, the lone survivor of the attack, who is in deep trauma at a city hospital,” Kabdule told AFP.
Warekar, who reportedly worked for a private firm in Mumbai, was able to carry out the attacks after lacing the food at the gathering with a sedative, according to several local media reports.
But the Indian Express newspaper said he stabbed his victims after they went to bed, having all decided to spend the night at the house in Thane.
“Prima facie evidence suggests that the accused bolted all the doors of the house and murdered his family while they were asleep with a knife that we found near his body,” Ashutosh Dumbre, joint commissioner of Thane police, was quoted saying.
Kabdule said he could not confirm whether the victims had been sedated, saying investigators were awaiting medical test results.
Footage showed men carrying bodies wrapped in sheets from the house to a waiting ambulance, as crowds and police gathered outside the white-walled home.
Kabdule said details of the attack “are still sketchy” along with the motive.
According to the Press Trust of India news agency, a property dispute was behind the killings, but Dumbre said initial investigations have so far found no trigger for such an “extreme step”.
“In our inquiry so far, no one has yet been able to give the reason for this,” Dumbre told the ABP news channel.
“He worked with a private company in Mumbai. There were no known financial troubles or disputes and now we are hoping that the lone survivor can tell us something about the trigger,” he said.