The sound of screams and clanging steel shattered the still darkness of the early Sunday morning. Altamash Warekar’s mother sent him to their neighbor’s house to investigate the noise.

When he arrived, he saw a young woman, blood streaming from her neck, who was banging a steel cup on a pot and yelling from inside the locked home: “Help! Brother has killed everyone,” she screamed, according to the Hindustan Times.

When police arrived soon after, they discovered 14 people lying dead, their throats slit. Another man — Hasnain Warekar, the alleged killer —  was found hanging in his room, a meat cleaver clasped in his hand, the Indian Express reported.

The young woman, Warekar’s 21-year-old sister Subia Bharmar, was the sole survivor of the killing spree in Thane, northeast of Mumbai. Her account has given authorities some sense of the bloodshed that unfolded Sunday morning, but they still have no idea what provoked it.

“In our inquiry so far, no one has yet been able to give the reason for this,” Ashutosh Dumbre, joint commissioner of Thane police, told the Indian news channel ABP. “… There were no known financial troubles or disputes and now we are hoping that the lone survivor can tell us something about the trigger.”

V.B. Chandanshive, the zonal deputy commissioner of police in Thane, told the Indian Express that the attack appeared well planned. Warekar used a newly purchased nylon rope to hang himself and had made sure that every window and door into the house was locked, police said.

According to the newspaper, Warekar, a 35-year-old accountant, had invited his relatives to his home that night ostensibly to celebrate his daughter’s fifth birthday. Warekar’s wife, children, parents and one unmarried sister, who all lived with him in the house in the village Kasarwadavli, just outside the city of Thane, attended the party. So did his three married sisters, who came in from out of town with their children.

When one sister rebuffed the invitation, he went to great lengths to persuade her to attend — he even paid her autorickshaw fare, an uncle, Mujeeb Warekar, told the Indian Express.

Meanwhile, Warekar explicitly told his brothers-in-law not to come until Sunday.

After dinner, the whole family went to bed. Police believe that Warekar may have drugged his relatives, because it seemed barely anyone screamed or even woke up during what happened next.

People carry the body of Indian man Hasnain Warekar, after autopsy from a hospital in Thane on the outskirts of Mumbai. (Rajanish Kakade/AP)

Around 2 a.m., the Indian Express reported, citing Thane police, Warekar slit the throats of his two daughters using a knife meant for slaughtering goats. Then he moved on to his sisters’ children. The oldest child slain was 16, according to the Hindustan Times. The youngest was his own daughter, a 3-month-old named Umera.

After that, Warekar allegedly turned on the adults: his parents, his sisters and his wife, Jabeen.

“His wife ran from the first floor to the ground-floor kitchen, where he eventually slit her throat as well,” a police officer told the Indian Express. “The fact that she must have shouted but no one awoke makes us suspect the food had some sedatives. Forensic reports will verify that.”

Dumbare told the newspaper that Warekar apparently bolted all the doors to the house before the attack, ensuring that none of his relatives could escape.

Thane is about 30 miles north of Mumbai

Bharmar, the lone survivor, was slashed on the face but managed to push her brother away before he could attack again, according to the Hindustan Times. She hid in a locked bedroom and screamed for rescue.

When Altamesh Warekar, the neighbor, arrived, he called for other villagers to help, he told the Hindustan Times. Unable to break down the locked door, the group dislodged a window grill and pulled the young woman to safety.

Bharmar was taken to a local hospital while police broke into the home to find the aftermath of a massacre.

Though the police investigation is still underway, the Indian Express reported that a dispute over property may have been behind the killings.

The newspaper also reported that Warekar had drugged his family once before; a deeply religious man, he had given medicine procured from a priest to several of his relatives, knocking them out cold, neighbor Danish Baharnal said.

“He was usually reserved, but after that incident he withdrew a little more into his shell,” Baharnal recalled of the poisoning.

The family was hospitalized when they woke up, but it didn’t appear that any charges were filed against Warekar in relation to the incident a few years ago.

Chandanshive told the Indian Express that authorities will be looking into that case as they investigate whether drugs were used in Sunday’s killings.

Despite all that, most who knew him described Warekar as genial and generous. He often hosted family dinners for his sisters, police said. And during festivals, people from the village would ask him to sacrifice a goat, since he already owned a cleaver.

“In fact,” his father-in-law Sufiyan Jalil Patel — whose daughter was killed — told the Indian Express, “because of his hospitality, people would remark that I have found such a great son-in-law.”

Patel said he hadn’t heard of any problems from his daughter, though he said his son-in-law had changed jobs recently.

On Sunday, neighbors gathered near the house as authorities carried out the 15 bodies, each wrapped in a white sheet.

The Warekars had been living in Kasarwadavli for generations. No one who knew them had ever seen this coming.

“The family seemed fine and all the relatives were close,” a villager told the Hindustan Times. “How could anything like this happen?”

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