WASHINGTON, D.C. – A U.S. Federal Grand Jury subpoenaed the work records of nine truck drivers at Mail Contractors of America Inc. in its ongoing investigation of the origins of two letters containing the poison ricin.

The first was sent to a South Carolina postal processing centre. The second was intercepted last fall before it reached the White House, its intended destination. Both contained about the new hours of service rules for truck drivers.

A copy of the letter sent to the White House, and posted on the FBI Web site, reads: “Department of transportation (sic) If you change the hours of service on January 4, 2004 I will turn D.C. into a ghost town. The powder on the letter is RICIN. Have a nice day,” and is signed “Fallen Angel.”

Ricin is a poison that is easily available but must be inhaled in large quantities to be fatal.

Mail Contractors, based on Little Rock, Ark., has about 1,400 employees most of them truck drivers, and has been hauling U.S. mail for more than 40 years. The subpoena sought driver logs, telephone records, delivery receipts and expenses, the Washington Post reported.