A couple and their 21-year-old daughter were found dead in a flat in Dhaka's Kadamtali area yesterday morning.

Police suspect that the three were strangulated to death after being sedated. The legs and hands of the bodies were found tied up.

The deceased are: Masud Rana, 50, a Saudi expat, his wife Mousumi Islam, 45, and their daughter Jannatul Islam.

The couple's elder daughter Mehjabin Islam Moon, 30, has been taken in for interrogation. The police suspect she was involved, Shah Iftekhar Ahmed, deputy commissioner of Wari Division of Dhaka Metropolitan Police, told The Daily Star.

Two more members of the family, Moon's husband Shafiqul Islam, 40, and their five-year-old daughter were found unconscious in the flat. They were undergoing treatment at city hospitals.

"The incident may have been the result of a family dispute," the police official said.

The DC said that Kadamtali police recovered the bodies from the first floor of a five-storied building on Rajjab Ali Sarder Road around 11:30am after Mehjabin called 999. "She admitted that she mixed sleeping pills with tea and later strangulated them," he said.

He said that the deceased's hands and legs were tied and police found marks of strangulation.

At the Mitford Hospital, Shafiqul told reporters that on Friday, they went to his in-laws around 9:00pm from their home in Baganbari area of Kadamtali. There, his wife Mehjabin served noodles and tea to all. He then fell asleep and could not remember anything else.

Shafiqul added that his relationship with his wife has not been going well for the last three months. Mehjabin's relationship with her parents was not good either, he said.

The DC said that Mehjabin's father Masud has been living in Saudi Arabia for nearly 22 years and he also has another wife there. He returned to the country four months ago.

In all these years, their mother raised the two daughters here.

"Mehjabin's husband Shafiqul developed a relationship with her sister Jannatul. Besides, there were disputes between them over money and properties. All these issues might have led to the woman to kill her family members," the police official said.

He said that the detainee was in shock and that they would interrogate her gradually.

Talking to this correspondent, Mehjabin's aunt Sonia Akhter blamed Shafiqul for the murders and the disputes.

She alleged Mehjabin married Shafiqul six years ago but for the last few years, he has been harassing her younger sister Jannatul.

To escape from him, Jannatul was even kept in a "safe home" for five months two years ago, she said.

"He [Shafiqul] wanted to grab all the wealth of Saudi expat Masud Rana by marrying his two daughters," she alleged.

She added that Shafiqul was accused in a murder case in Keraniganj and to fight the case, he took Tk 8.50 lakh from Mehjabin's mother, which she provided by selling off her property. This is also one of the reason's behind the familial disputes, she added.

The OC of Kadamtali police station said Shafiqul, his wife, deceased Mousumi and Mousumi's sister had been accused in the 2016 murder case. 

A neighbour told The Daily Star that the family, which has been renting in the building for four years, mostly kept to themselves.

Sources in the DMCH said the autopsies would be carried out today.