Transcript for Envelope suspected of holding ricin addressed to Trump: Authorities

First, the suspicious and alarming letters tonight. The secret service just reporting they did intercept a suspicious envelope sent to president trump, saying the mail never made it to the white house. And we have also learned tonight of two other envelopes at the Pentagon that tested positive for ricin, the potentially deadly poison. One of them addressed to defense secretary James Mattis. Tonight, that Pentagon facility is now under quarantine. All oe letters being investigated. And ABC's chief global affairs correspondent Martha Raddatz leads us off. Reporter: The secret service intercepted a suspicious envelope on Monday addressed to the president. The envelope was intercepted before reaching the white house. Two other envelopes sent to secretary of defense Jim Mattis, the other to a member of the joint chiefs, the head of the Navy, admiral John Richardson, field tested positive for ricin. This is the Pentagon mail facility where letters are scanned every day. They are now quarantining all mail received yesterday. If these two gentlemen opened these envelopes and they got enough of it in their system, it could have harmed them. Reporter: Ricin is found naturally in caster beans, and in its purest form, can be deadly. In 2013, letters addressed to president Obama and other officials did contain ricin. A Mississippi man was arrested and is currently serving a 25-year jail term. So, let's get right to Martha Raddatz live us with tonight. And Martha, I gather the FBI will conduct another set of tests. We know sometimes there can be false positives. And the other big question tonight, are all of these letters related? Reporter: Exactly, David. Clearly, the envelopes themselves will be very helpful evidence, but also, they will look to see if the three letters are linked somehow. But there's a lot of testing that remains to be done. David? Martha Raddatz leading us off tonight. Martha, thank you. Next, to the race against

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