The Montgomery County Police Department had been rattled Wednesday night by a strange killing in a shopping center parking lot. A man was shot at long-distance with a rifle, a rare homicide for a suburban agency that liked to boast on its Web site that "violent crime is not regarded as a serious problem in this county."

The Glenmont slaying seemed an isolated mystery, and the next morning most officers were headed to the funeral of a colleague who had been felled by a heart attack. En route, Cpl. Paul Kukucka braked his squad car at a red light at Aspen Hill Road and Connecticut Avenue. He turned his head to see a woman running from the Mobil gas station on the corner, arms flailing.

"This man has just been shot! He's bleeding!" she yelled.

Kukucka jerked the car to the roadside and sprinted to the gray Presidential cab still parked at the pumps. Premkumar Walekar lay on the concrete, blood pouring from his chest. Kukucka started CPR, holding the dying man in his arms.

He reached for his radio and called it in.

It was the instant when chaos and chance turned into a terrible sort of clarity. News of the Mobil shooting ricocheted through the department on scanners and radios, bringing the random events of the previous night into focus: a round fired into a Michaels crafts store in Aspen Hill, only a few blocks away; the shooting in the parking lot of a Shoppers Food Warehouse; now the gas station shooting, another single shot fired from a distance.

"It quickly became a realization of our worst fears, that this was a continuation of what happened last night," said Capt. Barney Forsythe, head of the major crimes division.

It was a day that would thrust a suburban county police department into the national spotlight, as Montgomery's police matched wits with an unseen killer who seemed to flit across the county like a ghost.

It was 8:30 a.m. The killer had Sarah Ramos, who was settling onto a blue metal bench in front of a shopping center post office, in his sights. Lori Lewis Rivera, who was planning to vacuum the interior of a minivan, had little more than an hour to live.

More Dead, but Few Clues 

The killer's day had begun even earlier than police knew.

Gary Huss, body shop manager at Fitzgerald Auto Mall on Rockville Pike, heard a loud bang just after 7:30 a.m. and saw James L. "Sonny" Buchanan Jr. stagger through a gate in the fence. Buchanan, who had been mowing a short strip of grass alongside the curb, was clutching his chest and gasping for air.

Buchanan made it about 200 feet before collapsing, face down. The shop workers called 911, reporting that a lawn mower had apparently exploded. They decided not to turn him over for fear of injuring him further.

"I put my hand on his shoulder and said, 'Help is on the way,' " said service director Al Briggs. "But he was already gone."

When emergency personnel turned Buchanan over, they found a gaping wound in his chest, just below his heart. It was a gunshot wound.

Dispatchers sent out calls around the county: two dead. Minutes later, there were three.

"Possible suicide at Leisure World," read the message on Capt. Nancy Demme's pager. Officers at the scene knew immediately that the victim, 34-year-old Ramos, was not a suicide. She had been killed by a single bullet round so powerful that it passed through her head and into the window of the Crisp & Juicy chicken restaurant behind her.

Three killings, three locations, 56 minutes: The killer was working proficiently.

Police Chief Charles A. Moose ordered top officers to meet in a police bus filled with computer equipment at the Mobil station. Worried that the sniper would strike again during rush hour, Moose told police to blanket major roads in the area -- Randolph Road, Georgia, Connecticut and New Hampshire avenues. He instructed his staff to put on bulletproof vests.

News of the shootings spread, and state, regional and national law enforcement agencies called in to offer help. Maryland Park police dispatched officers to neighborhoods around schools. Officers from other jurisdictions offered to cover patrol routes. A Maryland State Police trooper arrived, offering 39 troopers in marked cars.

There were now plenty of officers and experts on the way, but no sense of what their mission should be.

Moose asked the assembled staff members about similarities. What about the geography? What about the race of the victims? Are these hate crimes? Officers flipped through their notes, at first saying that Walekar, a dark-skinned immigrant from India, appeared to be a black man. James Martin, the man shot the previous night, was white. Ramos was Hispanic. Buchanan was white.

"We had nothing, nothing, nothing, on any of these," said Bill O'Toole, a deputy police chief. "There was no pattern, all the logical stuff, all the things that we look for, didn't exist. It's rush hour, and there's so many people out and we're not hearing from anybody, a description or [that] they saw somebody running with a gun."

But at Leisure World in Silver Spring, officer Cindy Prange found a Spanish-speaking landscaper working nearby, who said he saw a white truck with black lettering rush from the scene after the shooting. Two men were inside, he said.

Prange and fellow officers relayed the information to the temporary headquarters. There was an immediate decision to broadcast it on live television.

But before anyone could get in front of the cameras, the radio crackled to life again. Another single-shot kill, this time in Kensington. The shooting site, a Shell station on Connecticut Avenue where Lewis Rivera had died while vacuuming the minivan, lay on a direct route from the Leisure World shooting -- and right past the police's temporary command post. It appeared the killer had driven by them, a bit of audacity that stunned the officers.

The body count was now five, and the time wasn't yet 10 a.m. Moose called schools to discuss a lockdown. Deputy chief O'Toole thought briefly of his wife, who worked at a bank near the Shoppers store and his 9-year-old son, a fifth-grader at a Gaithersburg school.

"This is our community, too," he said. "We're unnerved, we're angry, we're shocked. We've got all these resources coming in, and we don't know what we're looking for."

Stopping White Vans 

At 10:12, spokeswoman Demme faced the cameras.

"We're experiencing a crime, an ongoing crime that we have not experienced before," she said. She listed the killings hurriedly. Then she mentioned the white van for the first time, even asking hovering news helicopters for help.

Minutes later, the ping-ping-ping of the bell alerting workers in the 911 center that calls are holding -- a sound usually only heard during snowstorms -- began to trill nonstop. More than 2,000 calls poured in, overwhelming phone lines.

A psychiatrist from New York phoned to say that she thought the shootings sounded like a script from the TV show "Homicide." A man from California suggested they use the Amber alert system used for child abductions to put out an alert on the shooter's vehicle.

And it seemed everyone in the Washington area called about the vehicle.

"I saw a white van," a caller would say.

"Did you see a van, like a minivan?" Peg Maryn, a dispatch center supervisor, asked time and again. "We're looking for a box truck."

"What's a box truck?" the caller would ask.

Within minutes, police were pulling over so many white trucks -- guns drawn -- that spokeswoman Joyce Utter had to return to the airwaves, fearing innocent but confused motorists might be in danger.

"I urge people who are stopped by a police officer driving this type of vehicle: Follow the officer's instructions to the letter so you're not hurt and the officers aren't hurt. It's a high-risk traffic stop," she said.

Across the county, Montgomery State's Attorney Douglas F. Gansler called an emergency meeting over the office intercom. Forty of the office's 63 prosecutors -- everyone who wasn't in court -- crammed into a small conference room.

Gansler asked prosecutors to think about recent defendants: Did they know of anyone who said he wanted to get back at the world? 

They looked at a map. The slayings were geographically centered, but random. It suggested a different psychology from an irate employee opening fire in an office, and different from the school shootings at Columbine, in which the motive might be a vicious form of payback.

Who would have a motive to shoot innocent, apparently unconnected people in so many different places? 

"You start to look for patterns, and the pattern here was location and methodology," Gansler said. "They were all [shot] from distances with a high-powered rifle, and the victims were totally unrelated to each other. You're looking for patterns because you don't know who it is or why."

Not long after the fifth shooting, Gansler noted the time.

"It's been an hour and a half," he told someone in the office. That was the longest amount of time the shooter had gone without striking.

"It's been two hours," he said again later.

"After that point," Gansler said, "I remember thinking 'Maybe there won't be any more.' " 

After four shootings in two hours, there came a lull. Moose assessed the day for a fearful populace.

"This is a situation that's different and very bizarre to all of us," he said in mid-afternoon. "We're all concerned. We're all fearful. We don't know what we have at this point. . . . Nothing like this has ever happened in Montgomery County. This is a very safe community. Our homicide rate just increased by 25 percent in one day."

Grief at Nightfall 

At 7 p.m., with no new shootings and no leads in sight, police brought the families of the victims to a classroom at the county's public safety training academy.

Forsythe, the head of the investigation, spoke in a slow, calm voice. He promised that police would not rest until the killer was caught. He said his prayers were with them. He asked them to pray for police.

The husbands of the two dead women are Central American immigrants. Their story is one of bitter irony.

"They related to me how much they loved this country, how they had left their countries because they were so afraid of the violence," said officer Luis Hurtado, the police department's Hispanic liaison. "They came here to start a new life, and this happened to them."

Rivera's toddler flitted from one person to another. Every so often, the little girl, who has her mother's blond hair, offered her distraught father a hug.

The meeting wound to a close. The officers and the families went outside into the darkness.

The killer was out there, too.

Less than an hour later, Pascal Charlot, 72, fell dead at the intersection of Georgia Avenue and Kalmia Road NW.

He lay in the District, a half-block from the Montgomery County line.

Staff writer Nurith C. Aizenman contributed to this report.