Jamshedpur: A debt-ridden businessman poisoned his wife and six-year-old son and then hanged himself in an elite residential neighbourhood of the steel city, the incident coming to light on the couple's wedding anniversary morning on Tuesday and sending a rude jolt to family and friends.

Police have found as many as 12 suicide notes at the 3BHK Vijaya Gardens flat in Baridih. These are addressed to various individuals and organisations from whom 40-year-old Nishant Kumar Singh had borrowed an unspecified amount of money. One such note also has a cheque stapled to it.

While preliminary investigations indicate double murder and a suicide, a dupatta hanging from another fan in another room has homicide sleuths perplexed for now.

Nishant's elderly mother, Taramani Devi (68), who lives in an adjoining flat on the second floor of Sunflower tower at Vijaya Gardens, was the first to discover the bodies of her son, daughter-in-law Munni Singh (35) and grandson Master Akshak around 7.30am.

"I knocked on the door first, but there was no response. I pushed it hard and it opened," a wailing Taramani told reporters, adding that the door wasn't bolted from inside; instead, it was blocked by a sofa.

"I saw my daughter-in-law and grandson lying on the bed, lifeless. In another room, my son was hanging from the ceiling fan with a white dupatta. Today was their eighth marriage anniversary. Why did all this happen?"

Birsanagar police, led by OC Upendra Narayan Singh, inspected the murder and suicide scenes followed by city DSP A.K. Singh.

"Three deaths have taken place in the apartment. It is a suspected case of double murder and suicide. The man poisoned his wife and son before hanging himself. He left a dozen suicide notes, indicating he was burdened by loans," OC Singh said, adding that one of the suicide notes had a post-dated cheque of Rs 1.3 lakh stapled to it.

In another suicide note, addressed to his elderly parents Taramani and N.K. Singh (74), Nishant wrote that he was leaving this world with his wife and son, and no one was responsible for their deaths.

OC Singh said the intriguing part of the whole tragedy was in the third room where a red dupatta was found hanging from the ceiling fan. A foldable steel ladder stood nearby.

"Nishant Singh's parents have told police that they do not have any financial problem (while the suicide notes say otherwise). We have called in forensic experts," the officer said.

A relative said Nishant ran a canteen at the ESI Hospital in Adityapur and also had a fabrication business with Tata Steel's Jamshedpur and Kalinganagar (Odisha) plants among his clients.

"Nishant's parents are natives of Bihar. The elderly couple returned to Vijaya Gardens from their hometown only two days ago. They wanted Akshak to stay with them last (Monday) night, but the boy's parents didn't allow that apparently because he had his final exams from today (Tuesday)," the relative said.

Akshak was only a kindergarten student at Jamshedpur Public School in Baridih.