Officials at the Pentagon said that two packages suspected of containing Ricin were sent to Defense Secretary Jim Mattis and Admiral John Richardson, the Navy’s top official. From Fox News:

The packages never made their way into the Pentagon, but were flagged in a mail delivery building next door, the spokesman said.

Initial tests were positive for ricin, a posion made from castor beans, but the FBI is now currently doing analysis to make final determinations.

“On Monday, the Pentagon Force Protection Agency detected a suspicious substance during mail screening at the Pentagon’s remote screening facility,” Col. Rob Manning said in a statement. “The envelopes were taken by the FBI this morning for further analysis. All USPS mail received at the Pentagon mail screening facility yesterday is currently under quarantine and poses no threat to Pentagon personnel.”

Ricin is a poison that can take several different forms, but as a purified powder it can be deadly. It’s also one of the easiest poisons to manufacture.

According to the Centers for Disease Control and Prevention, if it is made into a partially purified material or refined, ricin can be used as a weapon capable of causing death under certain circumstances.

In June, a Wisconsin mom was accused of spreading ISIS propaganda online — including directing one person how to make ricin and how to deploy it at a government facility or water reservoir.

That same month, an Islamic extremist ricin attack planned for Germany was foiled.