He was handcuffed and led away by his colleagues.
A CCTV video of the incident revealed that the former cop was trying to rob a policeman as the latter was drawing money from an ATM.
The deceased was identified as Constable Abdul Wadood, posted at the security division of the Islamabad police.
The cop was attacked when he was coming out of a hotel after having lunch.
The accused was able to run away from the incident site.
Fresh standard operating procedures (SOPs) have been conveyed to police personnel.