An envelope sent to the White House tested positive for cyanide at an off-site mail screening facility on Tuesday, according to a statement from the Secret Service, The New York Times reports.
The statement said the envelope arrived at the screening facility on Monday, and tested negative for biological agents. But officials said the letter returned a "presumptive positive for cyanide" on Tuesday and was transported to another site for further testing.
Cyanide is a deadly chemical compound that makes the body unable to use oxygen.