He pointed his vehicle toward Interstate 75, merging into the traffic of metropolitan Atlanta rush-hour commuters listening with growing horror to radio reports of his bloody rampage.

Mark O. Barton, a chemist turned day-trader, was no stranger to violence. Six years earlier, his first wife and mother-in-law had been bludgeoned to death in a camper. At this very moment, his second wife and his two children were lying dead in nearby Stockbridge, their bodies still undiscovered.

Behind him, at the shiny office complex called Securities Centre, nine people were dead, a dozen more were wounded, and walls were splattered with blood. By nightfall, Barton would himself be dead, slumped over his steering wheel in the parking lot of a BP gas station.

At least one person saw signs of trouble on Tuesday, when Barton picked up her grandson for a Boy Scout meeting.

``Something's weird about this man,'' Marsha Jean DeFreese remembers thinking when the 44-year-old Barton, a troop leader, came to pick up her grandson Brian, who was friends with Barton's 11-year-old son Matthew.

Mrs. DeFreese had lived near the family last year in the Atlanta suburb of Morrow, before Barton split with his second wife, Leigh Ann. Mrs. Barton had moved to a Stockbridge apartment.

Sometimes, Mrs. DeFreese recalled, Barton would not return with the boys until 11 p.m., which she thought was strange. She chalked it up to their closeness.

Still, it was hard to tell. Nearly six years ago, Barton's father-in-law, Bill Spivey, had considered Barton ``the perfect son-in-law.''

Then the bodies of his daughter and wife -- Barton's previous wife, Debra, and her mother, Eloise Powell Spivey -- were found bludgeoned in a camper on an Alabama lake over Labor Day weekend.

Barton was the main suspect at the time. No arrest was ever made.

Around 3 p.m. on Thursday, Barton walked into the Momentum Securities brokerage office in the seven-story Securities Centre building in Atlanta's upscale Buckhead neighborhood. Armed with 9 mm and .45-caliber handguns, he started shooting with both hands. People huddled beneath desks, but four of his initial shots killed.

Barton then walked east across the six lanes of Piedmont Road and began shooting in the office of the All-Tech Investment Group, a stock trading firm in the Piedmont Center building where Barton had been a client.

Before he left, five more people were dead. Some workers threw a computer through a window, trying to escape. Others ran out; many remained holed up inside, waiting to be evacuated by police.

Sitting outside one door was Nell Jones, an attorney. ``He was ... very calm and determined, no feelings,'' she said. He pointed a gun at her and pulled the trigger at point-blank range. The bullet whizzed by her head.

Joette Castronova, 27, was one of the first paramedics at the scene. She quickly found herself holed up in an office with a 24-year-old man who had been shot. ``He was in a lot of pain. I just rubbed his head and told him he was going to be OK,'' Ms. Castronova said.

Outside, Atlanta police set up police lines and started an office-by-office, floor-by-floor search. Helicopters took to the air as the manhunt was broadcast live on national TV.

But Barton was long gone.

Miles south, the manager of the Bristol Green apartment complex in Stockbridge was thinking about the strangely quiet apartment unit in building 1300. The rent was late, and he wondered what was up.

He called Henry County Police at 3:23 p.m., less than 30 minutes after the shooting started in Atlanta, and let an officer in.

After seeing one body, the officer called for backup.

Both 11-year-old Matthew and 7-year-old Mychelle Elizabeth were dead, apparently from blows to the head. They lay in their beds, all but their faces covered. A handwritten note rested by each child's body.

Their stepmother also was dead, stuffed in a closet and similarly covered, with another scribbled note. In the living room was a longer letter, this one apparently typed out on the computer Barton so loved.

Barton, meanwhile, was across the city, heading north.

Stopping at the Town Center Mall in Atlanta's northwest suburbs, he approached a woman in the parking lot and tried to take her vehicle, threatening to shoot her if she screamed. She ran and contacted mall security.

Police pursued Barton's dark green Ford Aerostar up Interstate 75. About five miles from the mall, Barton pulled off into the BP station near a car wash.

Police were directly behind his minivan, surrounding Barton with guns drawn. Barton remained inside, still armed.

He put both guns to his head -- one behind each ear -- and fired, said Acworth police officer Steve Eidson. Moments later, he was dead.

``I'm just glad one of our officers didn't have to shoot him,'' said Acworth Police Officer Mark Camp.

Back at the lushly landscaped Securities Centre, evacuated office workers watched from police lines. Some huddled under nearby trees; others made their way across the street to El Azteca, a Mexican restaurant, where they ate dinner, sipped drinks and watched the investigation unfold.

``To think that when I woke up this morning, I thought that it was going to be a normal workday,'' said Tiombe Holland, 23, who works for a health services company one floor above some of the shootings.

For the second time in a matter of hours, a forthcoming Mayor Bill Campbell calmly related what he knew, what he didn't, how he felt. ``Pray for our city,'' Campbell implored on national television.

Two hours after the suicide, Barton's body was still at the gas station, still in his van, the driver's side door open. Nearby, a crowd of several dozen gawkers jostled to get a look.

Some explained why they were there. They wanted to get a glimpse of a mass murderer.