Bullet fragments taken from a customer fatally shot at a service station in Prince William County on Wednesday evening were conclusively linked yesterday to the sniper who now has claimed seven lives in nine days and has changed the way the Washington region goes about its everyday chores.

Although authorities had suspected all along that the sniper was responsible for the death of Dean Harold Meyers, 53, a Gaithersburg engineer, they confirmed it only after ballistics tests matched fragments from Wednesday's shooting to the .223-caliber bullet fragments removed from the bodies of several previous victims, officials said.

Like the two shootings before it, the Prince William attack occurred next to a major highway, allowing the killer to come and go quickly, a shift from the seven earlier shooting incidents.

However, investigators said they did not find a tarot card or any other communication from the killer as they did at Monday's shooting site, at a Bowie middle school. They also did not find a shell casing, as was the case in Bowie.

Confirmation that the sniper had struck for the second time in Virginia and the first time in Washington's more immediate Virginia suburbs widened the circle of fear that has caused many residents to go about their most mundane activities with caution. Gov. Mark R. Warner (D) urged people to be alert to their surroundings and be vigilant about the whereabouts of their children.

Prince William Police Chief Charlie T. Deane said: "Everyone has been keeping their fingers crossed that this would be resolved before the next one. And we certainly hope that there won't be a next one."

The shooting at a Sunoco station on Sudley Road, just off an Interstate 66 entrance ramp, was the ninth instance in which a person was struck by a single shot fired from a distance, the eighth shooting in a heavily trafficked shopping area, the third at a gas station and the third within a few hundred yards of a highway interchange. Two of the shootings were not fatal, and another shot was fired at a store, but no one was hit.

Deane said investigators believe the shot Wednesday night was fired from "some distance." Investigators said they were particularly interested in a patch of woods and high grass 50 to 75 yards behind the gas station and beside a Pargo's restaurant, where the snipermay have hidden in the darkness.

The police response to the shooting is another example of how life has changed since the sniper began his binge last week with five deaths in Montgomery County.

Immediately after receiving the call about the 8:18 p.m. shooting, police acted on the assumption that the sniper was involved. Instead of responding with a few units, local, state and federal officials swarmed the strip mall and intersection, shutting it down. Within minutes, Virginia State Police shut down the ramps to I-66, and troopers were posted along the highway.

They cordoned off a huge crime scene to look for evidence and had troopers, officers and detectives out in force corralling witnesses.

"The response was faster and at a higher level than it might be normally," Deane said. "We learned from the previous shootings that it's better to be too careful than to miss something that's potentially important."

Jeff Roehm, special agent in charge of the Washington field office of the Bureau of Alcohol, Tobacco and Firearms, said the Prince William response allowed his team to collect evidence without fear of it being compromised. "They clamped down and locked down and preserved the crime scene extremely fast, which minimized the chance of contamination," Roehm said. "It was all about the planning, and it clearly worked."

Deane said his department responded so quickly and with so many officers because he and other police chiefs had talked about the possibility of the sniper returning to Virginia. In the previous shootings, which left six dead and two wounded, the sniper struck targets in Montgomery County, the District, Spotsylvania County and Prince George's County.

All were struck by a single bullet to the torso or the head.

In Wednesday's shooting, Meyers was getting gas for the drive home from his engineering job when he was struck once in the left side of his head. Law enforcement sources said the bullet passed through his head, killing him instantly.

The sources noted that the sniper shot skillfully enough to hit Meyers as he stood in the narrow gap between a gas pump and his car. "While it's not an impossible shot, it still would have required at least some sort of training or hunting experience," said a senior law enforcement official. "It certainly wouldn't have been an easy shot."

The sniper was afforded an easy path of escape. The gas station, at Sudley and Balls Ford Road, is a few hundred yards south of an entrance ramp to eastbound I-66.

Some witnesses initially told police that a white paneled minivan left the area quickly and headed toward the interstate. But Deane later said the driver of the van had been located and appears to have a reasonable explanation for his actions.

If the police appear to have few solid leads to the killer's identity, it is not for a lack of information from citizens.

Thousands of tips flooded the new hotline (888-324-9800) yesterday being staffed by FBI agents and support personnel at the FBI's Washington field office. By late afternoon, agents had fielded about 500 tips considered worthwhile, said Chris Murray, a spokesman for the FBI.

The system was not without glitches. A flood of calls in the morning jammed the phone system for the entire field office for about three hours, making it difficult for tipsters to get through and for agents to field calls on other matters. Callers were often greeted with a message saying that all the circuits were busy. But by noon, the situation was corrected.

Initially, 24 people fielded calls. By early afternoon, there were 40, and later in the day, there were plans to add 20 more, authorities said. Murray said the tips were being fed into a computer and farmed out to the appropriate investigators.

In Prince George's County, where an eighth-grader was shot as he left his aunt's car to walk into Benjamin Tasker Middle School on Monday, hundreds of tips have come through the police department's Crime Solvers line.

In that shooting, the killer left a tantalizing clue: a tarot card with a message that said, "Mister Policeman, I am God."

Since then, police have been knocking on doors, conducting background checks of people whose names were phoned in by jittery residents and revisiting the scene of Monday's shooting a quarter-mile from Route 50, the major east-west artery between the District and Maryland. They have also been visiting gun shops and shooting ranges.

Many potential sources of clues have yet to be tapped. In Prince William, Deane said there are several surveillance videotapes from restaurants and gas stations that detectives hope will yield some sort of image of the sniper or his vehicle.

Although the sniper still is at large, prosecutors are thinking of the day they may face him in court.

Prince William Commonwealth's Attorney Paul B. Ebert, who has successfully prosecuted more death penalty cases than any other prosecutor in Virginia, said he believes the sniper would qualify for a capital murder charge under two Virginia statutes. One statute applies to criminals who have killed more than one person, and the other applies to terroristic acts.

"I've never seen an investigation as intense and as thorough and as far-reaching," Ebert said. "I'm sure that sooner or later, we will bring this person to justice."

Until an arrest is made, though, the tension is palpable. Several gas stations and restaurants near the Sunoco station were closed yesterday. Others were open, but their proximity to the crime scene hit business hard.

"It really affected my business," said Fred Freidouni, owner of the Battlefield Shell gas station diagonally across from the Sunoco.

"Also, people are scared. I had a lady this morning -- a regular customer -- she said, 'I'm scared to come out of my car to get coffee.' My daughter is scared to go to school. My wife is scared to go to work."

Trey Baker, 24, a construction worker from Fauquier County who stopped near the gas station for a bite to eat yesterday morning, said he has been looking over his shoulder when he's out.

"It's crazy. It makes you look around and watch what you do, but you don't know what to be aware of," Baker said. "You don't know where he is."

One bit of good news came from Children's Hospital in the District. Jacqueline Bowens, the vice president of government and public affairs at the hospital, said doctors "are hopeful [for] a full recovery" for the 13-year-old boy shot outside his school Monday.

The boy, whose name is being withheld by The Washington Post because he is considered a witness, remained in critical but stable condition at the hospital.

Wayne Curtis, a cousin of the boy, who is serving as the spokesman for the family, read a brief statement.

"He's a fighter. We remain optimistic," Curtis said. "Doctors have told us that this is a marathon, not a sprint. We are confident we will make it to the finish line."

A spokesman for the Orlando Magic basketball team said yesterday that all-star Tracy McGrady sent the boy a taped get-well message and an autographed jersey after learning that he had whispered the star's name to doctors this week. The team wants to fly the boy and his family to Orlando for a game when he is feeling better, the Magic spokesman said.

Authorities said their investigation is progressing, despite the careful and elusive adversary. They underscored that the more he roves around looking for targets, the more police agencies have a stake in his capture.

"We are going to solve this case -- whatever it takes," said Gary Bald, special agent in charge of the FBI's Baltimore office.

Staff writers Patricia Davis, Maria Glod, Annie Gowen, Hamil R. Harris, Fredrick Kunkle, Allan Lengel and Jamie Stockwell and staff researcher Bobbye Pratt contributed to this report.