Mark Barton, a former chemist turned day trader who had once worked out of the building, greeted the office secretary and then spoke to the branch manager. Initially he had been calm, friendly even, but his mood rapidly turned and he began referring to recent losses on the stock market.
Moments later Barton took out three handguns and opened fire indiscriminately on the staff who had once been his colleagues. His last words to those he killed were reportedly: "I hope this won't ruin your trading day."
Having shot dead four people and wounding many others and as people began running for their lives, Barton left the building, crossed the street, and then entered another brokerage firm where he again took out the .45, the 9mm and one other handgun he was carrying and shot dead five more people. He then fled - in a green van that disappeared in the busy afternoon traffic.
"There's an awful lot of blood everywhere," Atlanta's mayor Bill Campbell said, soon after arriving at the scene.
John Cabrer, a witness to the shootings, said he had seen many of those who had been hit, lying on the floor.
"I tried to administer CPR to one of them, but then I realised he was gone." he said. "So I went to the man who was still conscious on the floor and I called his wife for him."
Unknown to those police who and Swat teams which rushed to the business district in southern Atlanta, the trail of murder which erupted so dramatically in the middle of the afternoon had actually started several days and 35 miles to the south.
Exactly what happened at Barton's home in the suburb of Stockbridge, was still not clear last night. However, while police were refusing to confirm local media reports it seems Barton first killed his wife and two children - a boy and a girl - before packing his guns and heading downtown.
"It is believed that they are the wife and the two children of Mr. Barton, but that information will have to be verified," Mr Campbell added. "The indication from Henry County authorities was that the fatalities that occurred there occurred several days ago."
But as police last night said they had discovered Barton's body in his van in Cobb County, a surburb of Atlanta, it emerged that an indication of Barton's murderous potential may be buried as far back as 1994. Reports on local television said five years ago Barton was questioned by police after his first wife and her mother were found stabbed to death in Cedar Bluff, Alabama, where the family had been on holiday.
Barton, who in recent weeks had moved to Stockbridge from Morrow, another Atlanta suburb, was never charged for the 1994 killings but according to the mayor's office, he was considered a key suspect and was questioned for hours by police.
Jerry Wynn, a Douglas County sheriff's office investigator, said he had evidence that Barton had been having an affair and had taken out life insurance on his first wife.
"The motive here was a lot of anger. Kill, kill, kill," he said at the time.