The main post office was robbed and an office assistant killed at Zero Point in Bogra town.
The deceased is Prashant Kumar Acharya, 48, son of Ramkrishna Acharya of Bejora Uttarpara village in Shajahanpur, Bogra.
The incident came into light on Monday.
Superintendent of Police Sudeep Kumar Chakraborty said that investigation of the incident is going on with utmost importance.
Sadar police station Inspector (Investigation) Babu Kumar Biswas said that Prashant was performing duty as the night watchman was on leave on Eid. At some time on Sunday night, the robbery took place by cutting the grill and entering inside.
CID's expert team had reached the spot. Details of the robbed items would be confirmed when the magistrate arrives, he added.
Govind Acharya, brother of the deceased and another office assistant, has been taken into police custody for questioning.
Sadar police station Officer-in-charge (OC) Nure Alam Siddiqui said that the robbers broke the vault but probably could not take money from there.
Officials claimed that the money kept elsewhere was missing. If the magistrate comes and opens the vault, it can be confirmed about the loot.
The OC also said that the deceased office assistant Prashant had injury marks on his head. The autopsy report will confirm how he was killed. Besides, investigation is going on to find out whether there was any other reason behind the robbery.
However, the deceased's elder brother Paresh Acharya claimed that there was no incident of robbery. Many in the office did not like his brother so he was killed. A drama of robbery had been arranged to suppress the murder.
Rakib Bishas, assistant postmaster of the post office, said that besides the murder of Prashant, a lot of money was lost.