[1] Ricin is an extremely toxic plant protein that can cause severe allergic reactions, and exposure to small quantities can be fatal.

[1] The U.S. Centers for Disease Control and Prevention (CDC) states that 500 micrograms is the minimum lethal dose of ricin in humans provided that exposure is from injection or inhalation.

On January 4, 2004 new federal transportation rules took effect which directly affected the over-the-road trucking industry in the United States.

Called the most far-reaching rule changes in 65 years, the regulations reduced daily allowed driving time from 11 hours to 10.

The calculations were not allowed to factor in such delays as food and fuel stops and other time spent waiting at, for instance, a factory for a load.

[5] The text of the letter stated: Department of transportationIf you change the hours of service onJanuary 4, 2004 I will turn D.C into a ghost townThe powder on the letter is RICINhave a nice dayFallen Angel The Secret Service did not alert the White House, the Federal Bureau of Investigation (FBI), and other key agencies, including the CDC, of the discovery and positive tests until November 12.

[12] In the November 21, 2003 issue of Morbidity and Mortality Weekly Report the CDC recommended that until Fallen Angel was captured, "healthcare providers and public health officials must consider ricin to be a potential public health threat and be vigilant about recognizing illness consistent with ricin exposure".

[13] The discovery resulted in more than a dozen staffers undergoing decontamination as well as the closure of the Dirksen, Hart, and Russell Senate Office Buildings.

[13][15] The incident was treated as a criminal probe with investigators looking carefully for any connection between the ricin found at Dirksen and the "Fallen Angel" cases.

Postal Inspection Service (USPIS) and the Department of Transportation's Office of Inspector General fell instantly upon the "Fallen Angel" in the two letters.

[17] Federal officials, most notably at the U.S. Department of Homeland Security (DHS), remarked that the letters did not have the hallmarks of international terrorism and were more likely produced by a homegrown criminal.

[16] On January 4, 2004, the FBI, along with the USPIS and the DOT, offered a $100,000 reward in connection with the October 2003 case from Greenville, South Carolina.

[20] In February 2004, the United States Secret Service revealed a six-day delay between the discovery of the initial letters and informing the FBI and other agencies of their existence.

White House spokesman Scott McClellan told reporters that the letter was not determined a threat to the public due to it already having been intercepted.