The traders were returning to their neighbourhood after buying vegetables from the wholesale market in Manikganj’s Jaagir.
Bodies of 65-year-old retired high school teacher Anil Chandra Dash and his wife, 55-year-old Kalpana Das, were found inside the septic tank of their home in Rasulpur area near the district town.
Police said the couple’s only son, who works for a bank, lives in Dhaka.
Neighbours informed police about the deaths, said Tangail police OC Nazmul Haque Bhuiyan.
The police officer said they suspect the two were murdered some time during the night, possibly by men who barged into the house.
He, however, said further details will be available after an investigation.