Interior Ministry spokesman Sediq Sediqi said Tuesday she had displayed "unstable behavior" but that the investigation revealed no militants links so far.
On Monday, the policewoman identified as Sgt. Nargas shot 49-year-old Joseph Griffin, of Mansfield, Georgia, in what was the first such shooting by a woman in a spate of insider attacks by Afghans against their foreign allies.
The U.S-based security firm DynCorp International says on its web site that Griffin was a U.S. military veteran who had earlier worked with law-enforcement agencies in the United States. In Kabul, he was advising the Afghan police force.