The document is believed to have been written by Issa al-Hindi, an al-Qaeda operative captured in Britain last year. It recommends concealing bombs in limos because the vehicles "blend in" and "can transport larger payloads than sedans ... and do not require special driving skills." The limos can "access underground parking structures that do not accommodate trucks" and "have tinted windows that can hide an improvised explosive device from outside." The document calls for the deployment of three limos, each carrying 12 or more compressed-gas cylinders to create a "full fuel-air explosion by venting flammable gas into a confined space and then igniting it." It suggests painting the cylinders yellow to falsely "signify toxic gases to spread terror and chaos when emergency and haz-mat teams arrive."
Al-Qaeda used similar devices in the truck bomb that blew up the U.S. embassy in Dar es Salaam in 1998 and in a 2002 attack on a Tunisian synagogue. Shortly after the document surfaced last summer, the Department of Homeland Security began contacting limousine firms to warn of the danger. With hundreds of limos expected to jam the capital this week, authorities are on the alert.