The FBI has arrested a former sailor in connection with sending letters containing a suspicious substance to the Pentagon and White House, the Utah U.S. Attorney’s Office confirmed on Wednesday.

The suspect has been identified as William Clyde Allen III, of Logan, Utah, said attorney’s office spokeswoman Melodie Rydalch. Charges against Allen are expected to be filed on Friday.

Allen is a former damage control fireman apprentice, who served in the Navy from October 1998 until October 2002, leaving the service as an E-2, according to his official record. He was assigned to the combat support ships USS Detroit and USS Supply and his awards include two Navy “E” Ribbons, the National Defense Service Medal, and the Sea Service Deployment Ribbon.

The Pentagon received two envelopes addressed to Defense Secretary James Mattis and Chief of Naval Operations Adm. John Richardson on Monday. The envelopes initially tested positive for castor seeds, which is used to make a poison known as ricin, according to the Defense Department. Neither men were exposed to the substance.

Officials in the Defense and Justice Departments have declined to say whether the substance in the letters was toxic. It was also unclear on Wednesday whether there was enough of the substance in the letters to make people sick.

In addition to the letters sent to the Pentagon, the Secret Service intercepted a letter to President Trump dated Oct. 1 that also contained a suspicious substance, according to CNN.

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The letter never arrived at the White House and investigators are looking into whether all three letters are connected, the network reported. The Secret Service referred further questions on the investigation to the FBI, which declined to comment.

This article will be updated as we learn more.

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