Rockville, Md. ? Investigators hunting a sniper responsible for 10 attacks released their first wanted poster composite images of a white box truck after authorities confirmed Saturday that an eighth death was linked to the killer.

The images are the first of any kind to be released in association with a killer who has been stalking suburban Washington areas and targeting victims apparently at random. More than a week after the shootings began, a massive task force of county, state and federal officers still won’t say if they know who they’re looking for, or even if the sniper is acting alone.

“We’re putting information out, asking people to have their memories jogged,” said police Chief Charles Moose of Montgomery County, where five people were killed.

The two images, produced by the FBI based on witnesses from more than one shooting, show a flat-front white truck with a roll-up door in the back, a weathered paint job, a small dent in the back bumper and unknown dark purple or black writing on the side.

The witnesses were unable to provide the exact wording on the truck or the license plate number.

Moose said investigators also were working with witnesses to produce a similar composite sketch of a white Astro van with a ladder on the top that was reportedly seen leaving the scene of Friday’s deadly shooting at a gas station near Fredericksburg, Va.

Asked if the separate sketches meant the sniper may be using more than one vehicle, he said it “is not our goal to make any suggestions at all. We’re working with witnesses.”

The images were released as the reward for information in the case reached $500,000.

The latest victim was Kenneth H. Bridges, 53, a Philadelphia businessman and father of six who was shot as he pumped gas Friday morning at an Exxon station just off Interstate 95 in Spotsylvania County, Va., about an hour south of Washington.

It was a brazen attack, carried out with a single shot as a state trooper stood just across the street. Bridges fell to the pavement as gasoline continued to pump into his silver Buick.

The trooper rushed to help the victim, and the killer disappeared.

Montgomery County, Md., Police Chief Charles Moose holds up a composite image of a white box truck that police are looking for in connection with 10 sniper shootings. The two images were produced by the FBI based on witnesses from more than one shooting.

The attacks, all carried out in public places as the victims went about their daily tasks, raised a specter for area residents already shaken by last fall’s terrorist hijackings and anthrax attacks.

At least one high school homecoming and several Friday night football games were canceled by worried school officials in and around Washington, D.C.

Members of the Guardian Angels, the volunteer public safety organization, manned two gas stations in Alexandria to pump gas for travelers who were too scared to get out of their cars.

“We’re just trying to do our part to make people safe,” said John Ayala, the group’s Washington-area director. “People were calling us and saying, you know, what are you guys going to do?”

Schoolteacher Risa Silverman, 34, of Bethesda, Md., has kept her frightened students indoors for a week. When she filled her car’s gas tank Saturday, she sat on the floor of the car until the tank was full.

Her boyfriend lives in Israel, where fear is a daily necessity.

“I feel like I’m experiencing, somewhat, what they do every day,” Silverman said. “But here, there is no reason.”

Two composite images produced by the FBI of a white box truck are shown. Law enforcement officials are searching for the truck, believed to be linked to the sniper shootings in the Washington, D.C., region.

Clarence Shook, filling his truck at a Fredericksburg station just up the road from Friday’s shooting scene, said he keeps a 9 mm Ruger pistol under the dashboard.

“I’m not afraid,” he said. “But I am cautious.”

Each time, the sniper has fired a single round from a high-powered rifle, seemingly picking targets at random with no discernible links.

Tipsters have deluged toll-free hotlines, police stations and sheriff’s stations, but their information has yet to lead to the person or people responsible. More than 1,900 calls were received in the 24 hours after the shooting in Spotsyvania County alone, sheriff’s Maj. Howard Smith said Saturday.

Near the Exxon station where Bridges was killed, authorities knocked on motel room doors in their search for witnesses and possibly the killer.

One man who was questioned said investigators compared his face with a photo of a sandy-haired man.

“They thought I was the sniper,” said Hobert Epps, 36, of Athens, Ga., who said he was staying at a nearby motel.

Epps said investigators told him the picture was from a video surveillance camera near the scene of one of the shootings.

Reporters asked Moose repeatedly Saturday about Epps’ claim and about residents who may have seen the occupants of a white cargo van seen leaving the Exxon station. He said it has been his practice not to release such investigative details.

Moose, who planned to appear on four Sunday morning network talk shows, also warned members of the media not to follow investigators as they pursue tips in the case. He said such behavior could threaten the safety of witnesses.

“If you are engaged in that kind of activity, we ask you to please consider you may jeopardize this investigation,” he said. “We value our witnesses. … Their willingness to assist law enforcement may be at risk.”