A white powder contained in an envelope along with a threatening letter to the Elko County School District apparently is not toxic, Elko Police Chief Clair Morris said Wednesday.
Discovery of the letter prompted the closure of two post offices on Tuesday and sent two school district employees including Superintendent Antoinette Cavanaugh to a hospital for precautionary evaluation.
Morris said a team of military specialists from Idaho was flown in with equipment to make a preliminary assessment of the powder in a makeshift lab at the Elko Regional Airport.
The substance was sent to the federal Centers for Disease Control and Prevention for a more thorough analysis to determine what it is.
The FBI was assisting Elko officials in the investigation of what Elko Police Capt. Mike Smith called an act of domestic terrorism, which is a felony.
FBI Agent Todd Palmer said his agency was investigating "as it would any threatening letter."
While the first test of the substance indicated it could be some kind of contaminant, Smith said 70 percent of such tests can be inaccurate.
No one reported any ill effects.
Elko Postmaster Dan Deremiah said workers at the main post office and an annex who may have had contact with the letter were sent home to shower and wash their clothes. In all, about 50 postal workers were sent home early.
Smith didn't say what the letter stated. It showed up in the morning mail at the school district's main office.