Five days had passed since the last shooting, the longest break since the sniper began his lethal work three weeks ago. The sniper had never before struck on a weekend; if this was in fact the same gunman, he chose a rural town far from the capital to extend his reign of terror. The experts wondered: was he toying with the media and the authorities, trying to confound and confuse?

It has come to this: last week police were offering tips to Washington-area residents on how to avoid being killed by sniper fire. The advice, published in a box in The Washington Post, included: “When moving outside, walk briskly in a zigzag pattern.” People were not exactly zigzagging around the sidewalks and shopping malls, but many preferred to stay inside their cars at the gas pump, and not a few were too scared to venture out at all. Soccer games and outdoor fairs were canceled or moved onto secure military bases; cooped-up schoolchildren fidgeted as their mothers fretted in car-pool pickup lines. The police seemed stumped. One investigator sent his boss a pager message asking, “Is there anything else we can do?” The answer came back: “Keep praying.”

Last Friday evening, reporters buzzed over a possible break: a cleaning crew for a truck-rental company near Dulles airport had found a spent shell casing in the back of a white box truck. Was this the elusive vehicle spotted by several witnesses speeding away from several of the crime scenes? Officially, law-enforcement authorities were keeping silent until they received a forensic report from the lab. But hopes were fading by Saturday afternoon. “The shell casing is as much as a quarter of a century old,” a source close to the investigation told NEWSWEEK.

The murderer didn’t seem to fit any obvious pattern. He was more eclectic in his choice of targets than the typical serial killer, who generally settles on a type, like women with long hair, or black schoolchildren. This killer has slain a man in his 70s who was standing on the corner and critically wounded a 13-year-old walking into school. He appears to be race neutral, maybe deliberately so, alternating between black and white victims after the second day. And he has been far more methodical than a “spree killer,” who indiscriminately guns down his victims in one violent outburst. Investigators think that he probably lives in or near the Maryland suburb where he went on his first-day rampage–and that the keys to the case are most likely to be found there. But they can’t easily explain the rest of his bloody course to the east, south and west of Washington.

Naturally, people began wondering if the sniper was working for Al Qaeda. Armchair conspiracy theorists were busy. The shootings, all with one bullet each, had begun the day after White House spokesman Ari Fleischer somewhat cavalierly noted that Saddam Hussein could be disposed of for the price of “one bullet.” The sniper’s terror campaign came almost exactly a year after the anthrax letters paralyzed the mail and much of the U.S. Congress. With terrorism suddenly resurgent all over the world, it seemed plausible that Al Qaeda might want to ring the U.S. capital with random death. Could the shooter be a diversion before an even bigger and more deadly attack?

Most local law-enforcement officials were doubtful about Qaeda involvement. Still, “you’d have to be a moron to ignore the possibility,” one top local police official told NEWSWEEK. “Sniper attacks aren’t their M.O., but, prior to September 11, flying planes into buildings wasn’t their M.O., either.” Within the U.S. intelligence community, top officials were beginning to take more seriously a possible link between the sniper and global terrorism. “It’s a 50-50 chance that this could be Al Qaeda,” a high-ranking U.S. intelligence official told NEWSWEEK. Another top federal official said that it was impossible to put odds on a Qaeda connection. But this source confirmed earlier reports that a Qaeda detainee held in Belgium had told investigators that teams of terrorists, practicing at Osama bin Laden’s camps in Afghanistan, trained to assassinate American public officials (in one exercise, U.S. senators on a golf course).

It was probably just a disturbing coincidence that the shooter’s victim last Monday night was an FBI counterterror analyst. Linda Franklin, 47, a cancer survivor who was about to become a grandmother, had just walked out of a Home Depot in Fairfax County, Va., when a single shot rang out. Hit in the head, she crumpled to the ground. Too late, her husband, Ted, dived across her body. Law enforcement threw out a huge and carefully planned dragnet. Within five minutes, the first police cruisers were arriving at the scene. Helicopters were soon flying low overhead. Highways in all directions were roadblocked inside 15 minutes, massively tying up traffic. But the shooter slipped through.

Police were at least encouraged by the detailed leads provided by one witness. A man, who claimed to be ex-military, said that he had seen a gunman step out of a van, take aim with a rifle and shoot the woman from a range of about 40 yards. According to the witness, the shooter had climbed back into his cream-colored Chevy van with a ladder rack on top and a taillight missing and sped away. The sniper, described as olive-skinned, was said to be toting an AK-74, a Soviet-style assault rifle favored by bin Laden himself. Some investigators thought his story was a little too neat. How had the witness identified the gun make in the dim light? But the press ran with the witness’s account–until it turned out to be bogus. The witness, an ex-convict nicknamed Slim, had been inside the store at the time of the shooting. He was later arrested and charged with providing false information to police. They returned to search a wider area, but two days had been lost and a soaking rain had swept the scene.

Tracking down the killer may be a tedious process. Investigators are reviewing film from traffic cameras and sorting through thousands of phoned-in tips. They are poring over credit-card receipts from stores near the shootings, looking for common names. They are pursuing white vans the way Ahab pursued the white whale. Several witnesses thought they saw white vans or trucks leaving the scenes of some of the shootings. There are about 75,000 white vans or box trucks in the Washington area. Law enforcement has imported some high-tech help from the military: spy planes with sophisticated tracking cameras, radars and eavesdropping devices.

Some investigators cautioned against making the sniper larger than life. “We deal with guys like this all the time,” said one. “He’s just another bad guy”–and not even a particularly good shot. “My kid could make these shots,” the source said. From a range of a hundred yards or so, it is distressingly simple to shoot a person in the head or chest with any of about 30 weapons that can be easily purchased, along with various attachments, like sniper scopes. Of course, shooting someone across a crowded suburban parking lot with a massive manhunt ready to pounce–and getting away with it–is a matter requiring more skill. Police suspect that the sniper is using a device to mask the flash of his gun, NEWSWEEK has learned. Such “flash suppressors”–of no apparent use to a game hunter or target-range shooter–can be bought on the Internet for less than $10.

It is a distinct and disturbing possibility that the sniper may never be caught. According to the FBI’s Uniform Crime Reports, more than 500 people have committed sniper attacks (killing at long range) during the last 25 years. About 200 of those crimes–some 40 percent–were never solved. Police have been keeping a watch on perhaps a half-dozen men who seem the most suspicious. “Most crimes are solved because someone dropped a dime,” said a law-enforcement source. “There has to be a confluence of circumstances. Some guy calls and says, ‘My neighbor is acting strange.’ Not enough. ‘He’s acting strange and he has a white van.’ A little better. ‘He’s acting strange, he has a white van, he used to be in the penitentiary and last year I saw him strangle a kitten.’ Your ears prick up.” Perhaps police will get lucky or make a forensics breakthrough. But even if the sniper is caught, it is discouraging to think that copycats, including those loyal to bin Laden, may be watching and learning.