All four members of the family who were found dead in Rangpur city on Saturday were strangled to death while the disfigurement of their faces was caused by decomposition rather than any chemical substance, said Babul Kumar Biswas, the doctor who conducted their autopsies on Monday.

Babul Kumar, an assistant professor at the forensic medicine department of Rangpur Medical College Hospital, said there were no signs of chemical burns on the bodies.

"When a body decomposes, exposed areas outside the clothing can sometimes turn dark. This is part of the decomposition process," he told UNB over the phone in the afternoon.

He said the dark appearance of the victims' faces was caused by changes in blood and body tissues during decomposition and not by any chemical treatment.

"The faces did look dark but there were no signs of chemical burns," he said.

There were some minor injuries that may have resulted from a struggle, but nothing else significant was found, he said.

The clarification came after police found some liquid near the victims' faces and initially suspected that chemicals might have been used.

Rangpur CID police earlier described the faces of the victims as severely disfigured.

Sumit Chowdhury, Rangpur CID Superintendent of Police (in-charge) said on Sunday that investigators suspected possible chemical use because of the condition of the faces and the presence of liquid nearby.

They were killed at their home in Rangpur city after they allegedly objected to two young men taking Yaba on the rooftop of their house, police said on Sunday.

The victims were identified as Ganapati Chakraborty alias Jewel, 65, a former teacher of Rangpur Zilla School, his wife Pritilata Chakraborty, 50, their daughter Parthi Chakraborty Agami, 25, and their son Priyam Chakraborty Ayush, 12, a Class-V student of Rangpur Zilla School.

Rangpur Metropolitan Police Commissioner Mohammad Abdul Mabud disclosed the details of the gruesome murders on Monday at a press conference at his office in the morning.

Police arrested neighbours Siddhartha Das, 23, and Mugdha Das, 19, on Saturday night in connection with the killings.

They were produced before Rangpur Chief Metropolitan Magistrate Court-2 around 11:30pm on Sunday where their statements were recorded under Section 164 of the Code of Criminal Procedure.

Later, they were sent to jail.

On Sunday, Gopinath Chakraborty, elder brother of Ganapati Chakraborty, filed a murder case with Rangpur Kotwali Police Station.

Two accused made their confessional statements before Rangpur Metropolitan Magistrate Rafiq-ul Islam at around 11:30pm on Sunday, said Milon Chakraborty, Inspector (Investigation) of Kotwali Police Station and the investigating officer in the case.

He said the two accused gave their statements before the court, but the details were not disclosed in the interest of the investigation.