The minor was apprehended from his house today, they said.
Around 7 am today, the police were informed about the body of the security guard lying in the post office. The man was to retire next month, the police said.
According to Rajneesh Gupta, Deputy Commissioner of Police (Rohini), Saini's hands and legs were tied and his mouth shut with a tape.
There was an injury in the head inflicted by a blunt object. Hard disks of CCTV cameras and Rs 20,000 cash were found stolen from the post office, even as the accused could not break into the treasury.
Investigation revealed that guard was killed by his nephew on the night of January 25, they said.
Two hard disks, a mobile phone, the stolen cash and a broken bat, allegedly used by the accused to kill his uncle, were seized, they said.
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