A letter sent to the White House this week was laced with the lethal chemical cyanide, the Secret Service confirmed Tuesday night.
The White House Mail Screening Facility intercepted the letter when it arrived on Monday, the agency said according to CNN. Results from initial biological testing were negative.
"However, on 03/17/15, the chemical testing returned a presumptive positive for cyanide," Secret Service spokesman Brian Leary said. "The sample was transported to another facility to confirm the results."
Cyanide is a deadly chemical that manifests as a gas or in crystal form, the Centers for Disease Control and Prevention reported. It's often described as smelling like almonds, but not everyone picks up the scent. Exposure to large amounts can result in convulsions, loss of consciousness and respiratory failure.
No exposure concerns were raised for the person who first opened the package, described as "an envelope containing an unknown milky substance, in a container wrapped in a plastic bag," according to an alert sent to White House staff obtained by The Intercept.
The alert also said a man whose address was on the envelope is apparently the same person who once sent the White House a package covered in urine and excrement.
He has been known to the Secret Service for at least 10 years.
