The discovery of two identical vegetable knives at 3 Robinson Street has intrigued police as none in the De house is known to have cooked for over a year.

Sources said Partho De would be questioned for a second time in connection with the knives.

The two knives, found on a table in the living room earlier this week, looked "sharp and clean" - in contrast to other objects strewn across the ill-kept room.

One or two vegetable knives in a household are common but their presence in a house where a human skeleton and bones of two dogs have been found and whose occupants survived on cooked food brought from outside or uncooked rice and lentils soaked in water is bound to raise suspicions.

The human skeleton - believed to be that of Debjani, Partho's sister - was discovered on June 11 morning, hours after the charred body of the siblings' father Arabindo was found in a bathtub at the house.

"None of the guards of the house could recall having bought or brought the knives," an officer who is part of the team probing the Robinson Street case told Metro.

"The food bills and habits like eating uncooked rice and pulses soaked in water were an indication that no one in the family cooked or cut vegetables. The knives look relatively new and clean."

Another officer who had seen the two knives said they were "larger" than usual vegetable knives.

The police have also found a pair of scissors.

The knives and the scissors will be sent for forensic examinations to ascertain what they had been used for.

A police team had questioned Partho for over three hours at Calcutta Pavlov Hospital for the mentally ill on June 17. Partho has been at the hospital since June 11. The team is scheduled to question him again by the end of this week, sources said.

A senior officer not attached to the probe but experienced in handling homicide cases said: "The fact that the human skeleton found in Partho's room looked much older than what he had claimed hints at the possibility of the use of knives or other sharp weapons to remove masses of the putrefying body.

"Removing the masses would not only expedite the decaying process but also justify how Partho had managed to contain the stench from leaking out of the room."

The police, sources said, have also found certain writings dated June 6 and 7 - mostly of Arabindo - that need to be verified with Partho.

According to evidences collected till now, investigators have pieced together that something might have transpired on June 6 and 7 that prompted Arabindo to end his life.

"One entry suggests Arabindo might have had a fight - physical or verbal - with his son. The date suggests that it was right before Arabindo had penned down his suicide note on June 8," said a source.