WASHINGTON — Letters sent in recent days to the White House and to local law enforcement agencies in Texas contained the lethal substance ricin, and investigators are trying to determine whether 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 a detention facility and a sheriff’s office in Texas.
The envelope to the White House was caught at the final off-site 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.
The Joint Terrorism Task Force in Washington is leading the investigation, with assistance from New York, according to multiple law enforcement officials. So far, investigators have found no links between the ricin letters and any international terrorist groups, but the investigation is in its early stages, and nothing has yet been ruled out, one senior official said.
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.”
Officials declined to discuss what evidence they had that pointed them to the suspect. Gathering evidence will be a painstaking process. As part of the investigation, for example, agents may need to identify the sorting facility that handled the letters, identify public mailboxes assigned to that sorting facility and see if there is video of the suspect posting the letters in the hours before they were collected by postal workers.
This is not the first time that U.S. officials have been targeted in ricin attacks.
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 the secretary of the Air Force, Heather Wilson.
Officials determined that Mr. Allen had sent castor beans, rather than ricin. His case is still pending.
A year later, 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.
Adam Goldman, Zolan Kanno-Youngs and Eric Schmitt contributed reporting.