The complaint was lodged against PBI chief Banaj Kumar Majumder, its SP Naima Sultana, Chattogram SP Nazmul Hasan, inspectors AK Mohiuddin, Santosh Chakma and Enayet Kabir.
Of them, Mohiuddin is now assistant commissioner of Chattogram metropolitan police while Santosh Chakma is officer-in-charge of Khulshi police station.
According to the petition, Babul was called to the Chattogram PBI office and was handcuffed and blindfolded there last year. Later, he was tortured there as per order of the PBI chief, to make him confess to killing his wife.
Asked why are they lodging the complaint after so many days, Kamrul Islam said they refrained from filing case out of fear as those against whom the complaint is made are police officers.
However, SP Naima Sultana ruled out the allegation.
Babul's wife Mahmuda Akter Mitu was shot and stabbed to death in Chattogram city on 5 June, 2016.
Later, the police official, who is now in prison, filed a case over the murder immediately. In further development, Mitu's father filed another case in May last year, accusing eight people, including Babul.
The PBI is supposed to submit a charge sheet to the court within the current month.