WASHINGTON — An envelope that has tested positive for cyanide was intercepted Monday at the White House Mail Screening Facility, according to U.S. Secret Service officials.

The “initial biological testing was negative” on Monday, according to a statement by Secret Service spokesman Brian Leary, but on Tuesday “the chemical testing returned a presumptive positive for Cyanide.”

The Intercept first reported the missive’s discovery on Tuesday evening. According to The Intercept, the return address on the envelope matched the address for a man who a law enforcement document says has been tracked by the Secret Service for sending questionable packages as far back as 1995.

The sample has been sent “to another facility to confirm the results,” Leary said, adding, “As this is an ongoing investigation, the Secret Service will have no additional comment.”