After a day of alarm stemming from an apparent “suspicious substance” contained in mail received by the Pentagon on Monday and suspected to be ricin, Pentagon officials have identified the material as a widely available commercial precursor. “According to our preliminary analysis, the substance was castor seeds, from which ricin is derived,” Pentagon chief spokesperson Dana White told reporters on Wednesday. Castor-bean seed hulls contain ricin, but must be chewed to activate potential toxicity. The seeds are commonly available for purchase. Defense Secretary James Mattis and Admiral John Richardson, the chief of naval operations, were the intended recipients. White said the FBI is still investigating the incident. The Herald Journalreports a former U.S. Navy sailor suspected of mailing out the envelopes was arrested in Logan, Utah, Wednesday.