The techniques used by the Beltway sniper to evade capture during a three-week killing spree in Washington were also employed by a terrorist death squad in Ireland for as long as five years in the mid-1990s.
Police believe John Allen Muhammad and John Lee Malvo used a 1990 Chevrolet Caprice modified to hide a sniper's nest in the back seat and trunk, from which the pair allegedly killed 10 people and wounded three others in the Washington, D.C., area.
The Caprice's back seat folded down, sources told ABCNEWS, allowing the shooter to lie prone and aim from at least one hole in the trunk. All the attacks were accomplished with a single shot.
The method is remarkably similar to the tactics of a single-shot sniper who killed at least nine soldiers and policemen in the troubled Armagh border area of Northern Ireland starting in 1992.
"There's a striking similarity," said Adam Dolnik, a researcher who studies patterns in terrorist tactics and motivations at the Monterey Institute of International Studies.
The slayings ended in April 1997 when police swooped down on a farm and caught four members of the Provisional IRA, who were later described as a sniper team. Police believed two of them were the trigger men.
In their possession, they found weapons, radios — and a Mazda 626, which had a cavity in the rear from which a gunman could crouch and fire.
While the IRA sniper squad claimed a lower body count than the Beltway sniper, they were potentially even more threatening.
The Mazda used by the sniper squad was not only adapted as a firing platform, but it was, in the provocative language of one British newspaper, a "provo" tank.
It had been fitted with makeshift armor, to protect the sniper in case of return fire. The armor, stored in a concealed position, could be hoisted up behind the rear seats using a rope.
The sniper team also had another car, with a CB radio tuned to the same channel as the radio in the Mazda, presumably to be used as another spotting platform.
Police in the U.S. sniper case found a global positioning device, a laptop computer and a pair of two-way radios in Muhammad's car, according a federal criminal complaint filed Tuesday.
When the IRA sniper team was caught, the item that drew the most attention was the powerful Barrett Light .50-caliber sniper rifle the team had.
An American-made weapon specially designed for special operations forces, the gun weighs nearly 30 pounds, is almost 5 feet long, and fires 6-inch-long bullets that can strike a target from more than a mile away. It is also extremely loud — police also found ear plugs with the rifle.
Breandan MacSuibhne, a professor of Irish studies at Notre Dame, says the rifle was never used to its full potential. The sniper squad struck from only as far as 150 yards away, he said.
The IRA sniper team was found to be in possession of an AK-47, but local reports at the time pointed out the squad chose to use the Barrett because it can punch through flak jackets and concrete. It can even be used to disable vehicles.
When police arrested Muhammad and Malvo, they found a Bushmaster XM-15 rifle in the car, a commercially available version of the military's M-16. It has a maximum effective range of 600 yards, only a third of the Barrett's range — but the duo only used it to a range of 100 yards.
When police in Northern Ireland found the Barrett, they were delighted. It was in one piece, located in a secret compartment at the bottom of a trailer. They had feared the rifle would have been dismantled, making it harder for police to recover it.
When police in Maryland arrested Muhammad and Malvo, some reports said the Bushmaster rifle had also been hidden within the Caprice. They were also delighted because the rifle made a direct link between the two men and the shootings.
The Future of Counter-Terrorism
There has been no sign that the Beltway Sniper was in any way linked to the IRA, but there have been links between terrorists, even those whose causes are completely unrelated.
This spring, a House International Relations Committee hearing concluded the IRA has "well-established links" with terrorists in Colombia since at least 1998. Three Irishmen were arrested in Colombia in August 2001 on suspicion of training FARC rebels.
And even if the IRA didn't inspire Muhammad and Malvo, law enforcement experts fear the Beltway sniper will inspire others.
"This sort of thing is more dangerous and harder to fight than someone driving an airplane into the World Trade Center," said Terry Oden, a security consultant based in Birmingham, Ala.
Oden, who worked as the secret service attaché in Europe in the 1980s, recalled the IRA bombings. "Just imagine someone doing this in Dallas, New York, San Francisco," he said. "It's just scary, scary."
Dolnik was sure the Beltway sniper, owing to media attention, would surely garner copycats. In the years after the 1971 D.B. Cooper skyjacking, there were 40 similar attempts, he said — but none of them succeeded.
However, he was confident that al Qaeda would not be one of the copycats. "They're more of trend-setters than trend-followers," he said.
Meanwhile, Oden said it's too early to see what kind of counter-measures the sniper attack will inspire — but it's also beside the point.
An increased military presence — putting more personnel in the streets, and surveillance planes in the sky, like the kind the Washington-area authorities called on to find the Beltway sniper, might help, he said.
But ultimately, he made that the familiar analogy of likening security efforts to the war on drugs. "You have to stop it at the source," he said.