Two of the three suspects believed to be involved in a potential 9/11 anniversary plot against New York or Washington are Americans of Arab descent

Authorities are operating under the assumption that two of the suspects have arrived on U.S. soil, and they have been piecing together clues gleaned from flight logs and manifests, among other sources. A third suspect is believed to have been traveling through Europe, though it is not clear whether that person has arrived in the United States. American spy networks had intercepted communications of an attack from an al Qaeda operative in Pakistan, derived from a source who has provided accurate information in the past. The information suggests that the plan - thought to involve a vehicle-borne explosive device - is meant to coincide with the 10th anniversary of the September 11 attacks. The exact type of strike, however, is largely unclear. Authorities say that they have picked up "chatter," or widely divergent communications, from extremists that suggest the newly tapped al Qaeda head, Ayman al-Zawahiri, is in some way involved in the current plot. The plot is believed to involve three individuals and could include the use of a vehicle bomb, but "we cannot rule out other means," a U.S. official said. U.S. officials believe that operatives came out of the tribal Pakistan-Afghanistan border region - a volatile semi-lawless area that is home to extremist groups - and that they are part of al Qaeda "central." It is possible that Pakistan-based groups such as Lashkar e-Tayyiba or Tehrik-i-Taliban Pakistan could be involved.