FALLS CHURCH, Va. — A woman was killed outside a Home Depot store Monday night, and police were trying to determine whether the shooting was related to the sniper spree responsible for eight deaths in the region in the past 12 days.

“A female has been shot and killed,” said Fairfax County Police Lt. Amy Lubas. The woman was felled by a single shot at about 9:30 p.m., authorities said. All the other deaths were also caused by one shot.

A police spokesman said roads were being closed in the area, about 10 miles west of Washington, D.C. The Maryland task force investigating the sniper attacks was conferring with Fairfax authorities to see if Monday’s victim was the sniper’s ninth.

Virginia State Police said they were on the lookout for a white Chevrolet Astro van, last seen traveling east on Route 50 from Falls Church. Interstates 66 and I-95 are nearby. Witnesses at some of the earlier shootings said a white van or truck left the scene.

The Home Depot is in the Seven Corners Shopping Center, a 450-thousand-square-foot strip shopping center with a parking garage. The center also has a grocery store, an electronics retailer and a pet supply retailer.

Kristin Reed, a supervisor at the Barnes & Noble bookstore in the sprawling strip mall, said six employees were locked inside the store with an FBI agent.

“Cops and cops and more cops,” Reed said of the scene outside. “There’s a lot of people walking around.”

Reed said no one heard the shot inside her store. But “a customer had just walked outside, then came back in and said ‘I think I heard a shot.”‘

The federal agent in the bookstore “hasn’t said anything to us. He was on the phone with someone,” she said.

Earlier Monday, the longest lull yet in the Washington sniper’s killing spree brought little relief as jittery residents flooded police with calls upon hearing car backfire, firecrackers or breaking glass.

“Everyone is edgy,” said Montgomery County Police Chief Charles Moose, who is heading the investigation. “People are hearing things that may normally be overlooked.”

President Bush said the “cold-blooded” attacks have made him sick to his stomach. “I weep for those who have lost their loved ones,” he said. “The idea of moms taking their kids to school and sheltering them from a potential sniper attack is not the America that I know.”

Four police squad cars rushed to a Silver Spring car dealership Monday after the window of a customer’s BMW shattered when he closed the door. The man dialed 911, thinking a bullet broke the glass.

“People hear a noise, they’re going to call — they want to put an end to this just like we do,” said Prince William County, Va., Detective Dennis Mangan.

Authorities in Baltimore, meanwhile, seized a white van and found an assault rifle, sniper manual and ammunition similar to the .223 bullets used in attacks that have killed eight people and wounded two others, WBAL-TV reported.

MSNBC reported that a tarot card was found in the van and a sign on the dashboard read “Gihad in America.” A tarot card was also found at one of the shootings.

The van’s owner was being questioned by police Monday night.

“At this time, the task force believes this is not related to our sniper incidents,” said Louise Marthens, a Montgomery County police spokeswoman.