An envelope mailed to the White House tested positive for cyanide, the Secret Service said.
The envelope arrived on Monday at a facility elsewhere in the Washington area that screens mail for the White House. Biological tests were negative, but a chemical test on Tuesday came back positive for cyanide, the agency said.
The envelope was sent to another facility to confirm the result.
According to the website The Intercept, a law enforcement alert said that the return address was for a man who has a Secret Service record dating to 1995, including sending a package covered in urine and feces.
The alert said that the envelope contained an “unknown milky substance” in a container wrapped in a plastic bag, The Intercept reported. The Secret Service had no further comment.