On the loose was a killer with a deadly eye and a powerful weapon. The shots have been fired from such long range–as far away as six football fields, police say–that there have been no eyewitnesses. And the aim has been near perfect. This is a “very skilled” marksman, says Bureau of Alcohol, Tobacco and Firearms Special Agent Joe Riehl, saying it is quite possible the killer had been trained by the military or the police. Investigators believe the killer is using a powerful rifle, the kind issued by armed forces and law enforcement.

Police were on the hunt for a white box truck with business lettering on the side, a vehicle seen speeding away from the scene of one of the killings. It is likely the sniper has an accomplice who is driving the truck, says Charles Moose, the police chief in Montgomery County, Md. But the only evidence police have for certain is those .223 bullets–which seem to be specifically chosen for maximum damage. “The devastation it is designed to do is significant,” says Agent Riehl. One gun expert says the .223 was “very popular in Vietnam.”

This is not the first time a random shooter has sparked fear in America. In the mid-1990s, a stalker with a shotgun haunted Washington’s northern reaches. And trained assassins have taken aim at specific targets before. But what sets this spree apart, and makes it especially terrifying, is the combination of skilled marksmanship with utter randomness. These are killings, it seems, with no motive, no purpose. Firing from such a distance, the killer knows of his victims only what he can see through the scope.

The victims, police say, were men and women from a mix of ethnic backgrounds, ordinary people doing everyday things. James (Sonny) Buchanan Jr., 39, was mowing the grass; Lori Ann Lewis Rivera, 25, was vacuuming her car; Premkumar Walekar, 54, was filling his car with gas; James Martin, 55, was walking out of a grocery store; Sarah Ramos, 34, was sitting on a bench near a post office; Pascal Charlot, 72, was standing on a corner. (Late Saturday, police announced that a 43-year-old woman, shot and wounded in Fredericksburg, Va., had been hit by the same shooter.)

After hearing a bang, Butch Parker, a mechanic, looked up to see Sonny Buchanan stagger and fall in a back lot of an auto dealership. As he yelled for help, Parker thought something had flown out of the lawn mower and struck Buchanan–there wasn’t a gunman in sight.

Each of the shootings occurred outside, near main thoroughfares. Five of the six killings took place in Montgomery County, upscale and suburban, a place where there are usually only two murders a month. But now communities are quaking. Schools in five districts quickly enforced “code blue” lockdowns–no one in, no one out, even for lunch and recess. After-school activities were canceled. Many parents kept their children home from school on Friday: absences soared more than 20 percent. “Everybody feels tremendous fear,” says Bonnie Beek O’Brien, a real-estate agent who lives in Cabin John, Md., but took the precaution of going to a more distant county to gas up her car. “I don’t know who or what to watch for.”

Police have stopped and searched so many white trucks they began slapping orange stickers on those that have been inspected. Trying to restore some sense of calm, officials by Friday were urging people to get on with their usual routines, like going to high-school football games. And so teams did square off on the gridiron, eager to forget for a while the rampage that has so spooked the region. But in the bleachers among the parents and students there were uniformed police officers–a reminder that a killer was still at large.