WASHINGTON — Letters sent in recent days to the White House and to federal agencies in Texas contained the lethal substance ricin, and investigators are trying to determine if other envelopes with the toxin were sent through the postal system, a law enforcement official briefed on the matter said on Saturday.
Investigators believe that the letters were sent from Canada, and have identified a woman as a suspect, the official said.
The letter to the White House, which was addressed to President Trump, was intercepted, as were the letters to the federal offices in Texas. It was not immediately clear on Saturday which federal offices were targeted.
The envelope to the White House was caught at the final offsite processing facility where mail is screened before being sent to the White House mail room, according to a second law enforcement official. The Postal Service irradiates mail that is addressed to the White House and other federal agencies in the Washington area, and the mail is sorted in a facility that samples the air for suspicious substances.
Ricin, which is part of the waste produced when castor oil is made, has no known antidote.
“The F.B.I. and our U.S. Secret Service and U.S. Postal Inspection Service partners are investigating a suspicious letter received at a U.S. government mail facility,” the F.B.I. said in a statement. “At this time, there is no known threat to public safety.”
In 2018, William Clyde Allen, a Navy veteran, was charged in a seven-count federal indictment for trying to send envelopes with ricin to Defense Secretary Jim Mattis, the chief of naval operations, Adm. John M. Richardson, the F.B.I. director, Christopher A. Wray, the C.I.A. director, Gina Haspel, and secretary of the Air Force, Heather Wilson.
Officials determined that Mr. Allen sent castor beans, rather than ricin. His case is still pending.
In 2011, four Georgia men were arrested and later sentenced to prison for plotting to spread the toxin simultaneously in five American cities, targeting federal and state officials. That same year, American counterterrorism officials said they were increasingly tracking the possibility that Al Qaeda would use ricin in attacks against the United States.
Two years later, a Mississippi man sent letters containing ricin to President Barack Obama and a Republican senator in an attempt to frame a rival. The letters were intercepted at sorting facilities.
In 2014, Shannon Richardson, an actress, was sentenced to 18 years in federal prison for mailing letters laced with ricin in May 2013 to multiple people, including Mr. Obama and Michael R. Bloomberg, the mayor of New York at the time.
This is a developing story. Check back for updates.
Adam Goldman and Zolan Kanno-Youngs contributed reporting.