KABUL, AFGHANISTAN - Sgt. Nargis went to work Monday with murder on her mind.

By the end of the morning, she would succeed, becoming responsible for this year's 62nd insider killing, in which Afghan security forces have killed U.S. or other coalition personnel. Such killings have greatly increased this year, but Nargis' killing of a U.S. police adviser, Joseph Griffin, 49, of Mansfield, Ga., 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 a jilted lover or a Taliban infiltrator, were 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, normally considered a plum job, one that is entirely underwritten by international aid, American and European, earmarked specifically 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 who, 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 interrogations after her arrest Monday.

What she would not say, however, was why she had done it, he said.

"We just don't know," Zaher said.

Seeking a victim

Her first stop was the Interior Ministry compound in downtown Kabul, where her own office was located. Zaher said she told questioners that she had prowled the compound looking for someone important enough to kill.

"She saw two foreign women on the grounds of the MOI, and thought of killing them," he said.

They were aid workers looking for police assistance in distributing warm clothing they'd collected for refugee children.

"She said she thought they were not worth killing," Zaher said.

So instead she went about half a mile, 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 confession, she gained access by hiding her weapon on her body -- women are searched much less thoroughly because of cultural norms.

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 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 placed the gun in her uniform pocket, where it would be more accessible. She tried to get into the Kabul governor's office and then the police chief's office but was turned away by guards both times. She told interrogators she wanted to kill either of them.

Nargis next went down to the ground floor, determined to kill someone, knowing she would be caught with the gun if she tried to leave.

Shot without warning

That is when she encountered Griffin, an employee of DynCorp International who began working with the Afghan police as a trainer in 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 shot Griffin in the head at close range, from behind, without any warning. Although he died at the scene, Afghan officials said, he was taken to a U.S. base by medevac.

As more detail about 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.

The only thing Afghan officials seemed to be certain of was that 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 Mujahid said 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."