Authorities have confirmed that the same high-powered weapon was used to kill at least three of five Maryland residents that were murdered in less than one day.

Ballistic testing was still under way to determine if two other shootings in Maryland are linked to the same rifle.

Police continued searching for two men in the sniper slayings and were investigating whether two other shootings were part of the same terrifying crime spree.

"You've got a driver, you've got a shooter," Moose said. Police said the description of men in a white van with dark lettering came from a witness to one of the murders.

Authorities were trying to determine whether a 72-year-old man shot to death Thursday night on a Washington street was connected to the Maryland slayings. And Friday afternoon, a woman was shot in the back as she loaded packages into her car outside a crafts store in Fredericksburg, Va., 55 miles south of here. She was hospitalized Friday night.

The Bureau of Alcohol, Tobacco and Firearms has also received a bullet casing from the Virginia shooting and will test it, Moose said.

The ATF is also examining evidence from Thursday's Washington shooting, in which Pascal Charlot, 72, of Washington, was killed while standing on a street.

"I'm not denying we have extreme interest, but we are going to wait for the science," Moose said.

Investigators determined Friday that the same weapon was used to shoot a cab driver at an Aspen Hill Mobil station, a woman at a Kensington Shell station, and another woman in front of a post office near a retirement community in Silver Spring, he said.

Police hunting for the killers pulled over white vans Friday and plastered orange stickers on the back to show the vehicles had been checked. Moose said investigators were chasing more than 200 leads.

Police also "very easily" eliminated as a suspect a man who turned himself in Friday morning in Arlington County, Va., and said he was responsible for the shootings, Moose said. The man was charged with giving false information to police.

Each Maryland victim was felled by a single bullet, apparently from a high-powered rifle or handgun. Police said evidence indicated the killer was some distance away and used .223-caliber bullets.

The search went on amid a mix of fear and defiance among residents of the economically and culturally diverse slice of the suburban county where the shootings occurred.

All over Montgomery County, people did what they usually do on a Friday, but they moved slowly and quietly, glancing at trees, bushes and rooftops. Many said they were afraid but wouldn't stop getting groceries, going to work or leaving their children with a baby sitter.

"I had to shop. I need to eat. I can't stay at home all day," said Kira Leonova, who works at a bookstore near one of the slaying scenes. "I have to work and I have a family."

Dexter Evans, 20, scanned the traffic as he waited for a bus to Rockville, and he took a second look at every white truck. "You can't even walk down the street without looking over your shoulder," he said.

Schools opened with extra police patrols and calls poured into 911 dispatchers about suspicious noises.

"People are on edge," Moose said. "We're all human. We're all afraid."

Officers have collected security camera videos from businesses near the shooting scenes. Moose said authorities were reviewing a surveillance tape from one of the scenes, declining to release details except to say "it has been helpful."

Joseph Riehl, spokesman for the federal Bureau of Alcohol, Tobacco and Firearms, said a person with reasonable shooting skills could accurately use a weapon with .223-caliber bullets from about 150 yards. Riehl said such weapons can be accurate up to about 650 yards.

All five victims died within five miles of one another during a 16-hour span Wednesday evening and Thursday morning. All were gunned down in broad daylight in very public places: two at gas stations, one outside a grocery, another outside a post office and the fifth as he mowed the grass at an auto dealership.

"There's still no information to lead us to think our victims are associated," Moose said. "They don't appear to be anyone's enemies, just random targets."

Carin Saez, 27, found herself going back to school Friday to pick up her 12-year-old niece, deciding it was too dangerous. Saez said she would not let her own children go back to school until the killer was caught.

"I was petrified to even go to the store last night," Saez said. "My kids were scared. They didn't even want to go outside. They're more scared now than on September 11."

Ruth Reyes, a teacher's assistant at Julia Brown Montessori School in Olney, was spooked.

"Now I feel like I can't stop at a traffic light," she said. "I turn my face and wonder, 'What is on my right and my left?' I don't know who is around me."

Officials at Richard Montgomery High School in Rockville canceled a Friday night pep rally and police were posted at the football game against rival Wooten High. Dani Young, a 17-year-old senior, said: "It kind of ruins the mood of homecoming."

In Bethesda, Mary Patterson said as she leaving home for a hair appointment: "I'm not afraid. After all, I'm 81 years old -- my time could be anytime."

Police are offering a $50,000 reward for information leading to the arrest of the "skilled shooter".

The Associated Press contributed to this report.