Shibendu Saha’s aunt Anita is brought to Charu Market police station on Monday morning. She and her husband Amalendu were denied bail in court and remanded in police custody till July 27. Picture by Pabitra Das

Calcutta, July 19: The murder of six members of the Saha family was not carried out in the manner originally presumed — an act of poisoning by a debt-ridden man who later hanged himself.

On Saturday night, Shibendu Saha killed his parents, his wife and two children and his brother before taking his own life in their south Calcutta home on Tollygunge Road.

Post-mortem of the bodies late on Sunday night revealed an array of disconcerting truths. Anubha and Simanta — Shibendu’s mother and his three-year-old son — were poisoned. Shibendu’s younger son, three-month-old Vedanta, appears to have died after being hit on the top of his tiny head. His wife Swati was poisoned and then strangled.

The seniormost member of the family, Shibendu’s father Nabendu, and his brother Krishnendu were poisoned and bludgeoned on the back of their heads with a blunt object.

Preliminary investigations and post-mortem reports suggest Shibendu took time to execute this elaborate devilish plan. Only after he was sure his mother and his elder son were dead did he proceed to conduct the next round of killings.

The entire act, police said, was spread over two-and-a-half hours — between 12.30 am and 3 am — after which, he hanged himself, taking the extra precaution of tying his legs with a towel.

Before that, Shibendu sent an SMS to sister Jayashree inviting her to go through the suicide note. The cellphone message was sent around 6.15 am.

On the basis of the note, where Shibendu narrates the family’s financial difficulties, the police late last night arrested his uncle Amalendu and his wife Anita. The two live in the same house on a different floor. Amalendu was a partner in the family’s business in wholesale supply of flour and semolina and making bakery products.

“To argue that a debt trap was the immediate compulsion is hard to accept. The loan amount was not astronomical — it was a few lakhs and could have been organised, given the assets available with the Sahas,” said an investigating officer.

While the chemical reports are still to come in, investigators said mercuric chloride was possibly used as the poison. Forensic experts said this compound, readily available at chemical shops, works in a flash on babies and the aged and is more potent than a handful of sedatives.

Once in the blood, mercuric chloride first affects the brain and then the heart, lungs and the kidneys. Unlike other chemicals, the only sign of poisoning by mercuric chloride is the presence of blood either at nose or the mouth, which was found on almost all of the deceased.

At the post-mortem, the investigators and doctors first stumbled upon the jarring truth that not everyone was poisoned. “Even if there are no external injury marks or even blood, a post-mortem would reveal if a victim has been hit by an object. In some of the cases, these signs were clearly present, besides the presence of poison in the blood,” said a senior officer of the detective department.