Montgomery County police headed to the site at Battlefield Sunoco, where the man had just finished fueling his car when he was hit, apparently by a single shot.
Although police could not say with certainty that it was related to the series of sniper killings, the similarities were enough to bring detectives from Maryland to the scene, trying to determine if it is number seven.
Virginia State Police said that two men were seen fleeing in a white Dodge Caravan after the Manassas shooting and that after issuing an alert they had found and interviewed a man in a black Honda they believed to be a witness.
Early this morning, Prince William County Police Chief Charlie Deane said the victim, described only as an adult white male, had put the gas pump handle back in its slot and was getting ready to leave when he was shot dead.
Deane said the man was not a local resident and that ballistic evidence will be analyzed by the federal Bureau of Alcohol, Tobacco and Firearms to see whether last night's shooting is the latest in the serial sniper slayings.
"At this point, we cannot say it is related to those shootings," Deane said. He said investigators had not determined the spot from which the fatal shot came nor how many shots were fired.
Police had cordoned off a six-block area around the gas station, where the body still lay six hours later.
"We are still very preliminarily beginning this investigation," Chinn said. "We have been in contact with the officials from Maryland and the task force there, so we are sharing any information we have."
Before last night's slaying, with the investigation in its seventh day, police had been analyzing a few scant clues - including a mysterious note that suggests the killer is taunting the detectives on his trail.
Frustrated by not only the fruitless search for the killer but also several days of intense news media attention, Montgomery County Police Chief Charles Moose angrily criticized reporters yesterday for disclosing the note's discovery.
Investigators say the note was found in woods near Benjamin Tasker Middle School, where the sniper shot and critically wounded a 13-year-old boy heading into school Monday morning. The message, scribbled on a tarot card known as the Death card, read, "Dear Policeman, I am God."
The Washington Post reported this morning that the tarot card also contained a handwritten request from the sniper that it not be revealed to the media. Sources were quoted as saying some detectives had hoped that if they honored the request, the sniper might communicate with investigators again.
Moose said the leak about the card to a Washington television station Tuesday night might have a "detrimental" effect on the investigation, which now involves nearly 200 investigators from several states and the federal government.
"This is an adjustment that we feel is unwarranted because we should have been able to control it," Moose said.
It is unclear what police have gleaned from the card or its significance to the gunman. Police discovered the tarot card next to a shell casing from a high-powered rifle in an area of flattened grass with a clear line of sight to the front of the school, law enforcement officials said.
ATF officials said the shell casing found next to the tarot card was .223-caliber, the same as in all the other shootings. They declined to discuss other forensic evidence in the case.
The scene suggests the sniper had been lying in wait for a victim, perhaps arriving under cover of darkness and staying hidden for several hours before the attack, officials said.