Sub-inspector Rafiuddoula of the police station filed the two cases accusing four unidentified people on Sunday night, said Muhammad Abdul Haque, officer-in-charge of the police station.
Besides, three bodies were handed over to the family members of the deceased on Monday.
They are Zahirul, 30, son of Lokman, Sabuj Sardar, 17, son of Khairul Sardar and Faruk Pramanik, 35, son of Jamaluddin Pramanik of Ataikula in Pabna district.
Earlier on Sunday evening, the body of another victim Lutfur Molla was handed over to his family.
Police recovered the bullet-hit bodies of four young men from Panchrukhi area on Dhaka-Chattogram highway in Araihazar upazila early Sunday.
Local people spotted the bodies in the area and informed the matter to police.
The faces of the bodies were smashed and bullets were found in their bodies, said police.
Police also recovered two pistols, one bullet and a private car from the spot.