A staffer at the John McCain for president campaign office in Centennial opened an envelope containing an unspecified threat and a white powdery substance on Thursday.
The office building where the office is and a neighboring officer were evacuated Thursday afternoon at about 4 p.m., and FBI, Secret Service and local authorities responded to the scene, located at 6334 S. Racine Circle.
As many as twelve people were exposed to the substance, but no one apparently reported suffering any symptoms. Four or five people took themselves to a hospital to get checked out.
Hazmat crews entered the building shortly after 4:30 p.m.
The City of Denver is at a heightened security level, as the Secret Service and other officials prepare for the Democratic National Convention, which is set to begin on Monday.