Police continued their feverish pursuit of the serial sniper terrorizing the Washington, D.C., area Friday after ballistics evidence conclusively linked the Wednesday night murder of a man at a Virginia gas station to the killer.

Montgomery County, Md., Police Chief Charles Moose said a special projects unit of the FBI was working "with a sense of urgency" on a graphic aid to be distributed to the public in the search for the sniper.

He and FBI officials declined to describe the graphic, but said it would be clear later Friday.

Authorities haven't said if tapes from the latest attack, at a gas station in Manassas, held any clues.

The latest victim, Dean Meyers, 53, of Gaithersburg, Md., was felled by a single shot Wednesday night after he filled his car's tank with gas in Manassas, where he worked for a civil engineering firm. Police said ballistic evidence developed Thursday linked Meyers' death to the sniper.

"This is crazy. It's too close to home," Michelle Rhoades, 19, of Triangle said Thursday night as she stopped at a gas station in Woodbridge, about 15 minutes from where Meyers was killed.

Rhoades said she refuses to live in fear, but admitted she scoped out the station, looking for woods where a sniper might hide, or a highway that would provide him a fast getaway.

For investigators, one potentially promising lead was the sighting -- again -- of a white minivan at the murder scene. The van was the most publicly touted lead police had, but they played down its significance late in the day Thursday. Prince William County Police Chief Charlie Deane said when the van was stopped, its occupants had a reasonable explanation for their actions.

Meyers' death broadened the scope of an investigation that has frightened residents in suburbs surrounding the nation's capital and has strained police in two states and in the District of Columbia.

Schools in many suburbs cancelled field trips and outdoor activities and were under heightened security. Residents were modifying their shopping habits, trying to ensure they wouldn't be the next victim.

Bebi Tasawar, the mother of three working in a glass-fronted 7-Eleven, said she was afraid to come to work Thursday night knowing the sniper had been within 10 miles of her store. It didn't help, she said, that the parking lot was unlit and that the store is adjacent to thick woods.

"When we throw the trash out, we're looking around. It's scary," she said. "You don't know when you walk out the door what will happen next.

"He could be watching us right now."

Just across the parking lot, Robert Evans was working security at a Sheetz gas station and convenience store. The station normally only has security guards on weekends, but he was brought in for an 8 p.m to 6 a.m. shift.

"I'm paying a lot more attention to the tree line," he said.

While pumping gas, Jerry Hughes continually shuffled around his car.

"I figure he's shooting at targets that are not moving, so if he wants to keep shooting at gas stations, I'll keep moving until my gas is pumped," Hughes, 42, said.

A toll-free hotline -- 888-324-9800 -- set up to accept tips was overwhelmed by calls Thursday. Police were advising callers getting repeated busy signals to be patient and to keep calling. Additional phone lines were being installed.

Still, police were deliberately vague about their evidence and leads.

"It's a difficult case but we are developing more information as the minutes go by," Deane told a news conference Thursday.

Manassas is about 35 miles southwest of the Maryland suburbs where most of the attacks happened. Meyers' shooting was the second in Virginia. A woman was wounded by the sniper last Friday in Fredericksburg, 30 miles south of Manassas.

Police in yellow slickers walked shoulder to shoulder Thursday through a drizzling rain, looking for evidence near where Meyers was shot. Deane did not say whether they had found anything, but said there had been no communication from the killer.

A tarot death card with the taunting words, "Dear policeman, I am God" was found near a shell casing outside a school in Bowie, Md., where a 13-year-old boy was critically wounded by the sniper Monday. Authorities have refused to discuss the card or any other evidence.

Meyers was a project manager in Manassas for Dewberry & Davis, a civil engineering firm. He had worked there for 20 years.

"He was quietly concerned about other people, and he never drew attention to himself," co-worker Dave Brent said. "He did things to make things happen and never took credit for it himself."

The Associated Press contributed to this report.