An envelope addressed to the White House has tentatively tested positive for cyanide after two rounds of analysis, the Secret Service said Tuesday. Additional testing will be necessary to confirm the finding.
The letter was received Monday at a facility that screens mail for the White House and is located away from the grounds of the executive mansion and its surrounding buildings in the heart of downtown Washington.
Initial biological testing came back negative, said agency spokesman Robert Hoback.
Additional testing conducted Tuesday returned a "presumptive positive" for cyanide.
The sample has been taken to another facility for further...