WASHINGTON, April 17 (UPI) -- The Anti-Defamation League said ricin -- in the news since a letter sent to a U.S. senator was laced with the toxin -- is popular with domestic extremists.
The deadly substance also may have been discovered in a letter mailed to the White House and to Sen. Roger Wicker, D-Miss., Tuesday.
Ricin is made from castor beans and is deadly if inhaled or ingested.
The letter addressed to President Obama at the White House contained a suspicious substance and was being tested, the Secret Service said Wednesday.
The letter arrived at the White House mail facility Tuesday, the same day it was announced a letter addressed to Sen. Roger Wicker, R-Miss., had tested positive for the poison ricin. The Wall Street Journal said officials indicated the letter to Obama initially tested positive for ricin.
There was a scare on Capitol Hill Wednesday morning when authorities evacuated parts of the U.S. Capitol complex because of suspicious packages found on the first and third floors of the Hart Senate Office Building and a suspicious envelope at the office of Sen. Richard Shelby, R-Ala., in the Russell Senate Office Building.
The suspicious packages were removed and Capitol Police reopened both buildings at 12:40 p.m., The Hill said.
Many ricin incidents have been attributed to homegrown extremists, particularly right-wing groups such as anti-government extremists and white supremacists. Other ricin incidents have been unrelated to any specific ideology, the ADL said.