An envelope containing the lethal compound ricin and addressed to President Donald Trump was intercepted earlier this week before it could reach the White House, law enforcement officials said Saturday, according to several news outlets, including The Associated Press.
The FBI, Secret Service and U.S. Postal Inspection Service are reportedly investigating the package’s source.
Ricin is a highly toxic substance found in castor beans. As little as one milligram of it can kill an adult, according to a Cornell University fact sheet about the compound. There is no known antidote.
It’s unclear whether the package — which investigators believe was sent from Canada — was intercepted before it reached the White House mailroom, The New York Times reported. The White House mailroom is located at a remote site elsewhere in Washington.
This article originally appeared on HuffPost and has been updated.