A policewoman who shot dead a US civilian aide at the police headquarters in Kabul on Monday is an Iranian national.
The woman, who is believed to have mental health problems, joined the security forces using an illegally obtained Afghan identity card.
The BBC reports investigators were not ruling out the possibility that she may have been in touch with "terrorist networks".
The woman , identified only as Nargis, 33, arrived at the headquarters on Monday looking for the police chief, the governor of Kabul or the head of the criminal investigation department.
When she was unable to locate them, she went to the canteen and fired one bullet at a NATO aide. She then shot at officers who tried to arrest her.
The interior ministry said an Iranian passport and Iranian national card were found at her house.
Her husband worked in the criminal investigation department. She graduated from the national police academy six years ago with the rank of sergeant.
The BBC reports that more than 50 NATO personnel in Afghanistan have been killed by Afghans wearing army or police uniforms in 2012.
Some of the attacks were carried out by Taliban infiltrators, others by Afghans. Often the precise motive is unclear.