A 19-year-old college student, Sabbir Sheikh, died after he was taken to Netrokona 250-bed District Hospital on 4 August.
The incident occurred near Harikhali canal in Netrokona Sadar উপজেলার at about 3:45pm.
Police said a nine-member district detective branch team was travelling by motorcycle towards an anti-narcotics operation when it passed the area.
Police said Sabbir and several others were gathered near the canal and ran after seeing the officers.
Police said several of the group fell into the water; the others swam ashore, while Sabbir went under.
Local residents brought Sabbir from the water to the roadside, and police took him to hospital.
Residential Medical Officer Mazharul Amin said Sabbir arrived at about 4:30pm with wet clothing and was declared dead after an ECG examination.
Amin said a post-mortem examination would determine the precise cause of death.
Sabbir's sister, Purnima Akter, said he could not swim, described his death as suspicious, and called for an impartial investigation and justice.
She said he was not accused in any case and was not involved in wrongdoing.
Detective branch Inspector Debangshu Kumar Deb said, based on what he had heard, that he saw no police fault in the incident.
Additional Superintendent of Police Hafizul Islam said police were examining why the youths ran, whether there was any connection to narcotics, and how Sabbir fell into the canal.