An envelope containing the poison ricin was sent to the White House, the New York Times reported on Saturday.
The newspaper said law enforcement believed the envelope, which was intercepted before reaching the White House mail room, was sent from Canada.
Ricin is a waste product in the making of oil from castor beans. According to guidelines from the federal Centers for Disease Control and Prevention, it “works by getting inside the cells of a person’s body and preventing the cells from making the proteins they need. Without the proteins, cells die. Eventually this is harmful to the whole body, and death may occur.”
Death from ricin poisoning, the CDC says, can “take place within 36 to 72 hours of exposure”, depending on dosage and whether the poison is inhaled, ingested or injected.
“It would take a deliberate act to make ricin and use it to poison people,” the CDC says.
The Times reported that investigators were working to find out if other envelopes containing ricin had been sent through the US mail.
The White House did not immediately comment.
Ricin has been sent to the White House before.
In 2018, a US navy veteran was arrested and charged with attempting to send ricin to officials including Donald Trump; the then defense secretary, James Mattis; the CIA director, Gina Haspel; and the FBI director, Christopher Wray.
In 2014, a Mississippi man was given a 25-year sentence for sending letters dusted with the poison to Barack Obama and other officials.
The same year, an actor was sentenced for 18 years for sending similar letters to Obama and Michael Bloomberg in a bizarre attempt to frame her own husband. The Guardian said the case was like “the plot of a cheap, pulp thriller – except perhaps not quite as believable”.
Ricin also featured in a famous case which could have come from a spy novel: the assassination in London in 1978 of Georgi Markov, a Bulgarian dissident who was pricked with a poison-tipped umbrella.