A third call about a suspicious white powder discovered on a letter has crews responding to the Oklahoma FBI headquarters, Thursday evening.
Investigators responded to the FBI HQ on 3301 W. Memorial Rd., shortly after 5 p.m. It was the third such call about a white, powdery substance discovered at a government building on Thursday.
Secret Service and FBI agents already responded to a scare involving a white, powdery substance at the U.S. Attorney's office downtown just after 2 p.m. At the time agents feared the white powder could be anthrax, but tests performed on the substance came back negative.
Emergency crews were then called to the federal courthouse, located at 200 NW 4th St. in downtown OKC about another white powder-coated letter just after 3:30 p.m.
Multiple units responded to the scene, as well as agents from the Oklahoma FBI. The courthouse was been given the 'all clear' shortly thereafter. Authorities are still testing the substance to determine what it is.
Agents are working to determine who mailed the letters to all three government buildings, but have not said whether or not they believe the three incidents are related.
Keep checking with News 9 and News9.com for more information.