Two of the accused have been arrested and Rs 25,000 has been recovered from them, said a senior police officer.
The incident was reported last night by two guards, Raj Kumar and Munna, who were deployed at the post office.
They made a PCR call and told the police that around six-seven men broke into the post office and held them captive and decamped with the bags, said the officer.
There was a large currency chest kept there but since the accused weren't able to open it after a few attempts, they didn't take anything from it.
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They took the loose cash that had come in the evening and hadn't been stored in the large chest, said the officer.
The accused persons took an auto-rickshaw towards Anand Vihar and got into an argument on sharing the booty.
When they were getting off the bus to take their motorcycles, two constables who were at the Anand Vihar police post found them to be suspicious.
The two accused, Deepak and Wasim, reside in Gautama Buddha Nagar in Noida.
Their call detail records are being scanned to identify their accomplices.
Police are suspecting that someone privy to the fct about the loose cash not being kept in the large chest could be involved in alerting the accused.