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Was she an Iranian agent, as Afghan officials suggested after they found her Iranian passport at home? Was she mentally ill? Even her interrogators were left perplexed.
Sergeant Nargis went to work with murder on her mind.
By the end of the morning, she would succeed, becoming responsible for the 62nd insider killing this year, in which Afghan security forces have killed U.S. or other coalition personnel. Such killings have greatly increased this year, but Sergeant Nargis's killing Monday of an American police adviser, Joseph Griffin, 49, of Mansfield, Georgia, ranks among the strangest.
Was she an Iranian agent, as Afghan officials suggested Tuesday after they found her Iranian passport at home? Was she mentally ill, as some police interrogators said privately and other Afghan officials speculated publicly?
The first theories, that she was either a jilted lover or a Taliban infiltrator, were firmly rejected by the authorities Tuesday, but even her interrogators were left perplexed by her motives.
Making the case even stranger was her job: a uniformed police officer attached to the Interior Ministry's legal and gender equality unit, what would normally be seen as a plum post, one that is entirely underwritten by international aid, both U.S. and European, earmarked for women's rights issues.
All she would tell her interrogators was that she went to work aiming to kill someone important and that she did not much care whom, officials said.
"I was myself asking her, trying to make her talk about what could make her do such a thing, and all she would say was she wanted to kill a high official," said Gen. Mohammad Zaher, the director of the criminal investigation division of the Police Department in Kabul Province, who attended her interrogation after her arrest Monday. What she would not say, however, was why she had done it, he said. "We just don't know."
Her first stop was the Interior Ministry compound in downtown Kabul, where her own office was. General Zaher said she had told questioners that she prowled the compound looking for someone important enough to kill.
"She saw two foreign women on the grounds of the M.O.I. and thought of killing them," he said. They were foreign aid workers who had been gathering warm clothing for refugee children and were looking for police assistance in distributing it. "She said she thought they were not worth killing."
So instead she went down the street and around the corner, about a kilometer, or half a mile, away, to the sprawling compound that includes the Kabul police headquarters and the Kabul governor's office.
There, according to Afghan officials and to what they said was her own confession, she gained access by hiding her weapon on her body -- women are searched much less thoroughly because of cultural norms and only by other women, who are often in short supply. As an official of the gender unit at the ministry, she probably had experience carrying out such searches herself and would know how to evade them.
Afghan security officials themselves have a well-founded fear of attacks by their own forces -- "green on green," or Afghan on Afghan, attacks have been even more common lately than attacks on foreign forces, with at least 14 Afghan police officers having been killed in such episodes in the past week. So even a uniformed police officer could not easily gain access to a building where she was not assigned.
According to the general's account, she first went to the restroom inside police headquarters, where she removed the gun from under her clothing and put it in her uniform pocket, where it would be more accessible. She then tried to get into the Kabul governor's office but was turned away by guards there because she had no appointment. Next, she tried the Kabul police chief's office and again was turned away. She told interrogators she had wanted to kill either of them.
Sergeant Nargis went downstairs to the ground floor, determined to kill someone immediately now that her gun was no longer hidden and she would be caught with it if she tried to leave.
That was when she encountered Mr. Griffin, an employee of DynCorp International who had been working with the Afghan police as a trainer since July 2011. Afghan officials said he had just bought an Afghan flag at a canteen in the police headquarters, for some sort of ceremony.
According to police accounts, she went up behind Mr. Griffin and shot him in the head at close range without any warning. Although he died at the scene, Afghan officials said, he was taken by medical personnel to a U.S. base.
As more detail about Sergeant Nargis emerged, it did little to shed any light on her motive.
Afghan officials at a news conference produced a copy of her Iranian passport, which showed she was 33 years old and, like many Muslim women in conservative areas, had only one name of her own.
She was a native of Iran, the officials said, and married an Afghan refugee in Tehran 10 years ago before moving to Afghanistan with him. He got a job as a low-level employee -- a tea boy, or servant -- at another department of the Interior Ministry. (Some officials said Monday that he was a police officer, though that proved untrue.) Sergeant Nargis joined one of the first classes of female police recruits in 2008 and would have had a much higher income than her husband.
Officials produced no evidence that Sergeant Nargis had any recent connection with the Iranian authorities, though there was plenty of innuendo, and some Afghan news outlets ran with the theory that she was an infiltrator. Blaming neighboring countries for atrocities in Afghanistan is a common refrain in the country, not less so because it sometimes proves to be true.
She and her husband, whose name had not been released, have three children, the eldest a son in his final year of high school, the authorities said. The husband was being detained as a witness but had not been charged with any crime.
Intriguingly, Sergeant Nargis returned to Afghanistan less than a month ago from a monthlong police training program in Egypt. While on that course with other female officers, she disappeared for two days without ever giving a satisfactory explanation for her movements, according to a police official who spoke to other police officers who had been with her. The official spoke on the condition of anonymity because he was not authorized to release information about the case.
The only thing Afghan officials seemed to be certain of was that Sergeant Nargis was not a Taliban infiltrator. Even the Taliban did not claim as much, in a statement issued by the group quoting a spokesman, Zabiullah Mujahid, and reported by the monitoring organization SITE Intelligence Group on Monday. But Mr. Mujahid did add that such attacks had been on the increase, not only by Taliban infiltrators but also by "Afghan soldiers who have an awakened conscience and feeling against the occupation forces."
That last theory resonated with one police commander close to the case. Either that, he said, or "she was just nuts."
A suicide bomber killed three Afghans on Wednesday in an unsuccessful attempt to enter a U.S. military base in eastern Afghanistan, Rod Nordland reported from Kabul, citing American and Afghan officials.
The attack on Forward Operating Base Chapman, located at an old military airfield just outside the city of Khost, came almost exactly three years after another suicide attacker succeeded in entering the base and killed eight people, most of them C.I.A. employees, in the deadliest episode for the agency in the course of the Afghan war.
Gen. Abdul Qayum Baqizoi, the police chief of Khost Province, said the attacker drove a minivan packed with explosives toward the front gate as civilian workers gathered to enter at the start of the day, but was stopped by an Afghan guard. He detonated his explosives and killed the guard, as well as two civilians, General Baqizoi said.
A spokesman for the NATO-led International Security Assistance Force confirmed the incident.