Two persons were later arrested and two other interrogated in connection with the recovery of skeleton.
Police said the skeleton tumbled out during clean-up operation of the tank at the residence of one Hazi Khairul Mollah at Chhatulia locality of the area.
Khairul and his brother were intially taken to Kasipur police station, under whose jurisdiction the area falls, but were let off.
Based on the statements of the family of a missing housewife in the neighbourhood, two family members of the missing woman's in-law's family were arrested, police said.
The gender and other details of the skeleton will be known after tests.
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