"For all intents and purposes, I think this case has been concluded," said Jimmy Mercer, the Atlanta police chief, yesterday morning, his voice still shaking from reading out the letters.
But the shock of Barton's killings will not dissipate quickly. Nor will the disbelief.
One more time, a prosperous community in America is coping with a bloody tragedy - this time leaving 13 dead, including Barton, and 20 injured.
The death trail began slowly and deliberately at the suburban apartment he had taken with his second wife, from whom he was estranged, and the two children from his first marriage. They were his first victims. But it ended in a mad and terrifying massacre on Thursday afternoon at the offices of two stocks and shares day-trading businesses on a gleaming business campus in Buckhead, a northern suburb of Atlanta.
In a spray of bullets from that the guns he held in each hand, he killed nine people before fleeing and later committing suicide.
What he left behind was one of the worst killing sprees in America's history and the bloodiest in the city of Atlanta.
It was also another first - an apparent massacre driven by fears about the stock market.
It left a tangle of questions and concerns, in particular about the pressures of "day-trading" on the stock exchange - a very mid-Nineties world, born of Internet technology and the bull market, to which Barton was deeply devoted. On Tuesday a cheque he wrote for $50,000 (pounds 31,000) to cover stock exchange losses bounced. He recently took a loss of at least $80,000.
Barton, 44, might have been the quintessential boring suburbanite. He was known for his broad smile but a private demeanour. He was a former scoutmaster. This week he had promised to buy his son a lizard so he could earn his cub scouts' reptiles badge. But there was something else out of the ordinary about Barton: in 1993 his first wife and her mother were hacked and beaten to death in a camping resort in Alabama. Barton was there and was the prime suspect. But charges were never brought.
Barton always asserted his innocence in those murders. This week he did so again in the first letter found by investigators in the living room of his family apartment in suburban Stockbridge.
"There is no reason ... to lie now," he wrote. But he was responsible for the unspeakable scene that awaited the police officers in the humble two- bedroom unit.
He directed them to the bodies, told them how he had killed them. And, again, he tried to explain why.
First, on Tuesday night, after she was asleep, he bludgeoned his wife, Leigh Ann. He wrapped the body in a blanket and stuffed it in a cupboard.
He then waited until Wednesday night to do the same to the children, Matthew, 11, and Mychelle, 7. He left them under blankets on their small beds with toys placed around them. He used a hammer on them, he explained, because it seemed a polite way to kill.
In addition to the longer letter, Barton left a short note with each of the bodies, expressing his love for them. He said he hoped to meet them in the after life. Reading them yesterday, police chief Mercer could not hold back his tears, and reporters also sobbed.
Of Leigh Ann, from whom he was separating, Barton said he killed her because she was "one of the main reasons for my demise". But there was regret after she was dead. Leigh Ann was then Barton's "honey, my precious love".
There was nothing to explain, however, what drove Barton to take the bloodshed so much further on Thursday. Wearing a shirt and khaki shorts he arrived at the All-Tech Investment Group shortly after 2pm, where he was heard to observe that it was a bad trading day (the New York stock market was indeed plummeting) and that "it was going to get worse".
Shortly before 3pm he opened fire. First he shot the manager and his secretaries before turning his weapons on the clients who were in to do their instant trades. Someone heard him exclaim: "I hope I'm not upsetting your trading day." Four people were killed.
Barton then fled across the busy, six-lane Piedmont Road to another building which housed the offices of Momentum Securities, where he had also been a client. There, after again commenting on the fact that it had been a bad trading day and that it was about to get worse, he continued the carnage, killing five more people and wounding several others.
"I saw a lot of blood in the hallway," said Chris Carter who works in the building. "There was a trail of blood leading from one end of the hallway to the other". An All Tech trader, Nell Jones, was at her computer when she heard the shots. He was, she said, "very calm and determined, no feelings". Officials said three of those hurt remained in a critical condition.
For Atlanta, it was another gruesome intrusion into high summer. In July alone, 23 of its citizens have died in mass killings. The worst incident, before this week, occurred on 12 July, when police found three adults, including the gunman, and three children shot dead in a family house in the city.
No one yet knows the precise nature of the depression that Barton said was afflicting him. It may have stemmed from the killings of his former wife and mother-in-law, but speculation continued to centre yesterday on his passion for day-trading.
Day-trading can be a heady combination of video poker and serious investing. Its practitioners play the markets minute by minute, shuffling stock holdings when they shift in price by just a few cents in a bid to accumulate profits.
The industry, of which All-Tech was a pioneer, has attracted about 5,000 users across the United States, some of whom do it from home and others in offices like the ones that became bloodbaths on Thursday. Experts have long warned that it is a risky pastime that can bring large losses and generate huge stress.
For a few desperate hours the authorities had no idea of Barton's whereabouts. In his letter to detectives he said he did not plan to live much longer and asked police to catch him and kill him. But that was not necessary.
At 7.45pm a police patrol car spotted his green Ford van in a town to the north-west of Atlanta and pulled it over into a petrol station. When they approached it, they saw that Barton had already killed himself.
A Time/CNN poll yesterday revealed that more than three- quarters of those interviewed were in favour of mandatory handgun registration, while some 61 per cent favoured stricter gun control laws.