The medical board, formed to examine the cause of death of three members and sickness of two others of an expatriate family in Osmani Nagar in Sylhet, has described it as a "mysterious" incident.
In the report submitted to the Sylhet Superintendent of Police on Thursday, the board said they did not find any evidence of sedatives or food poisoning in the bodies of the five persons
Police super Mohammad Farid Uddin Ahmad said "In the report of the medical board, this incident has been described as "death due to unknown and mysterious causes". Lack of oxygen might be a factor in their mysterious death."
There was no evidence of poisoning or use of sedatives in the bodies of the deceased and sick persons. Nor were external or internal injury marks found on their bodies, he added.
Vice-principal of the medical college, Professor Dr Shishir Chakraborty, head of the medical board, said on Thursday, "We made the report after reviewing the postmortem report, viscera examination, and food items recovered from their homes, medical tests reports of the sick, and after talking to the doctors who treated them."
Sylhet MAG Osmani Medical College Hospital authorities formed a medical board to determine the cause of deaths.
On 26 July, five members of a UK expatriate family were rescued unconscious from their bedrooms at a house at Osmani Nagar in Sylhet.
Police rescued them breaking down the doors and then sent them to a hospital where on-duty doctors pronounced Rafiqul Islam and his son dead. After 11 days, Rafiqul's daughter Sadia also died undergoing treatment at a hospital.
On 23 August, police described the death of the three expatriates in Sylhet as "an accident".
At a press conference, the Sylhet police super had said, "No evidence of any kind of chemical reaction or presence of poison was found in the bodies of the three expatriates in viscera examinations."
Mohammad Farid Uddin had said that during the investigation police questioned the relatives and neighbours of the expatriates, but no proof of previous enmity or attack was evident.
The police super also said the deaths might have happened due to smoke from the generator.
However, Rafiqul's wife Husnara Begum and son Sadiqul Islam returned home after recovering from sickness.
Deceased Rafique's brother-in-law Delwar Hossain later filed an unnatural death case with Osmani Nagar Police Station in this regard.