KABUL, Afghanistan – The policewoman who killed an American contractor in Kabul is a native Iranian who came to Afghanistan and displayed “unstable behavior” but no known links to militants, an Interior Ministry spokesman said Tuesday.

The policewoman, identified as Sgt. Nargas, shot 49-year-old Joseph Griffin of Mansfield, Ga., on Monday, in the first such shooting by a woman in a spate of insider attacks by Afghans against their foreign allies. Nargas walked into a heavily-guarded compound in the heart of Kabul, confronted Griffin and gunned him down with a single pistol bullet.

The U.S.-based security firm DynCorp International said on its website that Griffin was a U.S. military veteran who earlier worked with law enforcement agencies in the United States. In Kabul, he was under contract to the NATO military command to advise the Afghan police force.

Insider killings have eroded the trust between the foreign contingent and the Afghan government, just a year before most NATO troops are set to withdraw and turn security responsibility over to local forces.

The ministry spokesman, Sediq Sediqi, told a news conference that Nargas, who uses one name like many in the country, was born in Tehran, where she married an Afghan. She moved to the country 10 years ago after her husband obtained fake documents enabling her to live and work there.

A mother of four in her early 30s, she joined the police five years ago, held various positions and had a clean record, he said. Sediqi produced an Iranian passport which he said was found at her home.

“Her mental condition is not good,” he said, describing her behavior as “unstable.” He said that after she attended a recent training course in Egypt a “foreign government” — a clear reference to Egypt — informed Afghan authorities that she did not appear to be “normal.”

On Monday, senior Afghan officials said the policewoman was licensed to carry the weapon into the compound and was well known there. On Tuesday, however, the chief investigator, Gen. Mohammad Zahir, told reporters that she was not authorized to carry weapons into the compound but managed to pass through security checks with a hidden pistol. Zahir said the lapse of security was being investigated, as well as any connections to militant groups.