WASHINGTON, Oct. 3 (Xinhua) -- The FBI has taken a former U.S. Navy veteran into custody after pieces of mail with a suspicious substance addressed to the Pentagon, the White House and a senator's office were detected, raising poisonous ricin attack alerts, local reports said Wednesday.

Federal prosecutors authorized a probable cause arrest of the veteran William Clyde Allen in Utah, the U.S. Attorney's Office for Salt Lake City told ABC News. It's expected that a complaint will be filed on Friday in federal court in Salt Lake City, Utah.

Allen served in the Navy from 1998 to 2002 as a damage control fireman apprentice, Navy officials told Military Times.

Fox News on Wednesday quoted unnamed U.S. officials that a return address was the potential link to the former sailor.

Also on the day, Pentagon spokesperson Dana White said that the content in the packages that triggered the alert "appears to be castor seeds, from which ricin is derived."

"The FBI is still investigating," White said.

As least four pieces of mail were detected with a suspicious substance on Monday. Two received by the Pentagon mail facility were addressed to Defense Secretary Jim Mattis and Chief of Naval Operations Adm. John Richardson. The third was addressed to President Donald Trump in White House and the last one was to Republican Senator Ted Cruz's office in Texas.

Ricin, a poison found in castor beans, can be used in powder, pellet, mist or acid form. If ingested, it causes nausea, vomiting, internal bleeding of the stomach and intestines and can be deadly.