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US Defense Department personnel, wearing protective suits, screen mail as it arrives at a facility near the Pentagon in Washington, DC on October 2, 2018. - Two or more packages delivered to the Pentagon this week were suspected to contain the deadly poison ricin, an official said. Produced by processing castor beans, ricin is lethal in minute doses if swallowed, inhaled or injected and 6,000 times more potent than cyanide, with no known antidote. US Defense Department personnel wear the protective suits as a matter of routine. (Photo by Thomas WATKINS / AFP) (Photo credit should read THOMAS WATKINS/AFP/Getty Images)

US Defense Department personnel, wearing protective suits, screen mail as it arrives at a facility near the Pentagon in Washington, DC on October 2, 2018. - Two or more packages delivered to the Pentagon this week were suspected to contain the deadly poison ricin, an official said. Produced by processing castor beans, ricin is lethal in minute doses if swallowed, inhaled or injected and 6,000 times more potent than cyanide, with no known antidote. US Defense Department personnel wear the protective suits as a matter of routine. (Photo by Thomas WATKINS / AFP)        (Photo credit should read THOMAS WATKINS/AFP/Getty Images)

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US Defense Department personnel, wearing protective suits, screen mail as it arrives at a facility near the Pentagon in Washington, DC on October 2, 2018. - Two or more packages delivered to the Pentagon this week were suspected to contain the deadly poison ricin, an official said. Produced by processing castor beans, ricin is lethal in minute doses if swallowed, inhaled or injected and 6,000 times more potent than cyanide, with no known antidote. US Defense Department personnel wear the protective suits as a matter of routine. (Photo by Thomas WATKINS / AFP) (Photo credit should read THOMAS WATKINS/AFP/Getty Images)

US Defense Department personnel, wearing protective suits, screen mail as it arrives at a facility near the Pentagon in Washington, DC on October 2, 2018. - Two or more packages delivered to the Pentagon this week were suspected to contain the deadly poison ricin, an official said. Produced by processing castor beans, ricin is lethal in minute doses if swallowed, inhaled or injected and 6,000 times more potent than cyanide, with no known antidote. US Defense Department personnel wear the protective suits as a matter of routine. (Photo by Thomas WATKINS / AFP)        (Photo credit should read THOMAS WATKINS/AFP/Getty Images)

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US Defense Department personnel, wearing protective suits, screen mail as it arrives at a US government facility near the Pentagon in Washington, DC on October 2, 2018. - Two or more packages delivered to the Pentagon this week were suspected to contain the deadly poison ricin, an official said. Produced by processing castor beans, ricin is lethal in minute doses if swallowed, inhaled or injected and 6,000 times more potent than cyanide, with no known antidote. US Defense Department personnel wear the protective suits as a matter of routine. (Photo by Thomas WATKINS / AFP) (Photo credit should read THOMAS WATKINS/AFP/Getty Images)

US Defense Department personnel, wearing protective suits, screen mail as it arrives at a US government facility near the Pentagon in Washington, DC on October 2, 2018. - Two or more packages delivered to the Pentagon this week were suspected to contain the deadly poison ricin, an official said. Produced by processing castor beans, ricin is lethal in minute doses if swallowed, inhaled or injected and 6,000 times more potent than cyanide, with no known antidote. US Defense Department personnel wear the protective suits as a matter of routine. (Photo by Thomas WATKINS / AFP)        (Photo credit should read THOMAS WATKINS/AFP/Getty Images)

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HYATTSVILLE, MD - APRIL 16: An official walks past a hazardous materials response team truck outside a mail sorting facility April 16, 2013 in Hyattsville, Maryland. An envelope addressed to U.S. Sen. Roger Wicker (R-MS) tested positive for ricin at the facility where mail bound for the U.S. Capitol is sorted. (Photo by Drew Angerer/Getty Images)

HYATTSVILLE, MD - APRIL 16:  An official walks past a hazardous materials response team truck outside a mail sorting facility April 16, 2013 in Hyattsville, Maryland. An envelope addressed to U.S. Sen. Roger Wicker  (R-MS) tested positive for ricin at the facility where mail bound for the U.S. Capitol is sorted. (Photo by Drew Angerer/Getty Images)

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WASHINGTON - FEBRUARY 4: Members of a Hazmat team prepare to enter the Russell Senate Office Building on Capitol Hill, February 4, 2004 in Washington, DC. Three Senate office buildings are closed after a letter found in the Senate Majority leader Bill Frist (R-TN) office was cofirmed to contain the poison Ricin. (Photo by Mark Wilson/Getty Images)

WASHINGTON - FEBRUARY 4:  Members of a Hazmat team prepare to enter the Russell Senate Office Building on Capitol Hill, February 4, 2004 in Washington, DC. Three Senate office buildings are closed after a letter found in the Senate Majority leader Bill Frist (R-TN) office was cofirmed to contain the poison Ricin.  (Photo by Mark Wilson/Getty Images)