An inspector with the Delhi Police special cell was shot dead by his live-in partner at the latter's flat in Ardee City here on Saturday.
Police said inspector Badrish Dutt, a resident of Ashok Enclave in Faridabad, was shot in the temple with his service revolver by Geeta Sharma, a divorcee, who later shot herself.
The incident took place on Saturday between 1 am and 4 am.
The officer's body was found on the floor while Sharma's body was found over him. She had shot herself in the chin.
Commissioner of police (Gurgaon), Alok Mittal, said, "The two had been living together for just over a year and no suicide note has been found."
Joint CP Maheshwar Dayal said Sharma - who used to run a private detective agency - had recently been released after 20 days from Tihar jail.
Officers recovered her jail diary where she wrote that no one including 'B' had come to visit her.