The Pentagon has joined the search for the Beltway Sniper.
Defense Secretary Donald H. Rumsfeld agreed Tuesday evening to the FBI's request to use a military surveillance aircraft in the hunt for the killer, a senior defense official said.
The plan calls for having military pilots fly reconnaissance flights accompanied by federal agents, who would relay any collected information to authorities on the ground, the official said, speaking on condition of anonymity. A main objective is to improve communication among investigators.
Authorities had considered using a Predator unmanned aerial vehicle, but decided to use manned aircraft instead, officials said.
The help will be provided in a way meant to comply with the Posse Comitatus Act -- a 19th century law that bans the military from domestic law enforcement. That means the military will relay data to law enforcement and not decide on its own what targets to watch, the official said.
Defense officials told Fox News Channel that a special Army reconnaissance aircraft called an RC-7, based at Fort Bliss, Texas, would be sent to Washington. The aircraft is a modified DeHavilland DHC-7, adjusted to carry advance optics and communications gear for collecting intelligence on the ground, and it also carries advanced communications equipment to share with ground-based units. Currently, it's operated by six-man crews from the 204th Military Intelligence Battalion out of Fort Bliss, Texas. They are often used in counter narcotics operations in Latin America.
The aircraft would perform general reconnaissance, such as looking for or tracking the light-colored van authorities say was seen at one or more of the shooting sites. Pentagon participation also could involve a system of sensors that could detect flashes of gunfire on the ground, the official said.
More than half a dozen agencies already are working the case, a series of 11 random rifle attacks in 13 days that has killed nine people and seriously wounded two others. All but one of the attacks have been in neighboring suburbs in Maryland and Virginia. One was just inside Washington at the Maryland border.
In two recent killings, police threw up a dragnet near the shooting site, blocking off streets and expressway ramps and stopping traffic to check vehicles. The assailant slipped away.
Another official, who also discussed the matter on condition of anonymity, said that at the request of investigators, the Army has started searching its records for people trained as snipers for any former or current service member who might be involved in the shootings.
Law enforcement officials have not said they suspect anyone from the services. Experts have said the shooter also could be a hunter, a target shooter, someone with law enforcement experience, and so on.
Police from counties where the attacker has struck are participating in the joint investigation as well as both state police forces, Washington's metropolitan police, the FBI and the Bureau of Alcohol, Tobacco and Firearms.
By law the military is limited in the ways it can engage in domestic law enforcement, although state governors can call up National Guard troops for such missions.
Federal investigators refused Tuesday to rule out the possibility that organized terrorist groups are behind the shootings that have left some residents apprehensive all around the nation's capital.
"The communities are terrorized," said the homeland security director, Tom Ridge, and said federal investigators don't know whether the sniper might be a domestic or international terrorist or is working alone.
Asked whether there were links to Al Qaeda or other foreign terrorists, Ridge said, "I don't think we can foreclose that. Certainly, nobody in the FBI or the White House has foreclosed that."
Fox News Channel's Bret Baier and the Associated Press contributed to this report.