FBI and the United States Capitol Police were tasked to the investigation; like in the Fallen Angel investigation, the FBI was the lead agency. Detectives and agents focused on the possibility that the individual responsible for the 2003 letters was also responsible for the contamination at the Dirksen building. Within two weeks of the incident, investigators were questioning the validity of the positive ricin tests at the Senate building. The results raised suspicion because no source (e.g. a letter) was ever found for the ricin. It was possible that the "contamination" was from paper by-products and not ricin. However, later tests confirmed that the initial tests did not indicate a false positive and the substance was indeed ricin. By the end of March 2005, there were no suspects and no confirmed source for the ricin found in Senator Frist's office. Investigators also found no connection to the Fallen Angel case as of the same date. Despite those developments, investigators were not yet ready to declare a dead end to the investigation. As of 2008, no direct connection has yet been found between the Frist case and the Fallen Angel case and no explanation found for the origin of the ricin in Frist's office. See also 1984 Rajneeshee bioterror attack 2001 anthrax attacks April 2013 ricin letters Wood Green ricin plot Shannon Richardson, former actress who sent ricin letters to politicians in May 2013 References Further reading Anderson, Curt. "Ricin investigation expands to Tennessee, trucker radio", the Associated Press, via the Oakland Tribune via findarticles.com, February 7, 2004, accessed May 6, 2009. Crowley, Michael. "Paul Kevin Curtis and the Weird History of Domestic Ricin Terrorism", Time, April 17, 2013, accessed May 26, 2014. Eggen, Dan. "Letter With Ricin Vial Sent to White House", The Washington Post, February 4, 2004, accessed May 5, 2009. "Investigation of a Ricin-Containing Envelope at a Postal Facility — South Carolina, 2003", Morbidity and Mortality Weekly Report, November 21, 2003, Vol. 52, No. 56, pp. 1129–31. Kucinich, Jackie. "Ricin case 'still being looked at'", The Hill, September 15, 2005, accessed May 5, 2009. Schier, Joshua G. et al. "Public Health Investigation After the Discovery of Ricin in a South Carolina Postal Facility", American Journal of Public Health, Supplement 1, 2007, Vol. 97, No. S1, pp. 152–57, (ISSN 1541-0048) accessed May 6, 2009. External links Fallen Angel reward poster (FBI) (updated), Federal Bureau of Investigation, accessed May 5,