Two more people who were rescued from a vessel in Meghna river succumbed to their injuries at a hospital in Chandpur, rising the death toll to seven.
All of bodies bore cut marks from sharpened weapons with some having their throats slit.
Anisur Rhaman, medical officer at the 250-bed General Hospital, Chandpur, confirmed two more deaths to Prothom Alo on Monday afternoon.
Details of the deceased were unavailable.
Earlier, river police said they recovered the bodies of five people and rescued three other injured from a goods-carrying vessel that was anchored on the entry point of Ishanbala canal of Mengna river in Haimchar upazila of Chandpur a little after 3:00 pm.
Police and locals suspected miscreants might kill the vessel master and other crew on Sunday night. One of the injured who have his throat partly slit wrote his name Jewel on a piece of paper after being admitted to the hospital.
Chandpur deputy commissioner Mohammad Mohsin Uddin visited the hospital in the afternoon.
Earlier, Chandpur river police superintendent Syed Mushfiqur Rahman said these people boarded on the goods carrying vessel were killed by locally made weapons. Police suspect the incident might happen because of enmity.
He said they reached the vessel around 3:30 pm after receiving a call to national emergency helpline 999. They then found five bodies at five rooms and three others severely injured. The injured were sent to hospital for treatment.
All of eight people were on board at MV Al-Bakhera, which was owned by M/S HP Enterprise.