One key device, in use for only a few years and invented by Cherry under an FBI contract, is called the Percussion Actuated Nonelectric (PAN) disrupter. It hovers over the bomb like a praying mantis about to devour a bug. "It basically allows us to use an explosive to disarm an explosive," says Cherry, but that is as much as he will say about it, even though it is now used by bomb squads nationwide since the FBI distributed 500 free of charge last year. As described by Patrick J. Webb, a counter-terrorism supervisor for the FBI who was also on the scene and had tracked the Unabomber since 1982, the PAN disrupter is a long narrow stainless steel tube about an eighth of an inch in diameter, through which many different kinds of high-powered charges can be fired. The shock tube, as it is called, is manufactured in lengths up to 5,000 feet, so it can be cut to any desired length, letting the bomb squad remain at a safe distance from the explosive. When fired with a basic black powder round, as was used in this case, the PAN disrupter creates a flash that looks like a bolt of lightning, signaling that a shock wave is traveling down the tube. When the device performs correctly—Webb can't recall it ever misfiring—the shock wave will disable a key component of the bomb, such as the trigger, timer, or battery. The PAN disrupter, says Webb, is the only scientifically verified tool available to bomb technicians. It has been tested so many times with a variety of charges that technicians need only consult a guidebook that will correlate a bomb type to the correct charge, approach angle, and stand-off distance in which to use the disrupter. Fortunately, most bombs seen in the United States, about half of which are pipe bombs, are of simple construction. "We haven't seen a ramping up of sophisticated technology," says Webb. "We're still in the bomber Stone Age." Nevertheless, he acknowledges, the Unabomber had proved how deadly even primitive materials can be in a bomber's hands.