He'd been living there with his second wife, Leigh Anne, 27, and the children from his first marriage, Matthew, 11, and Mychelle Elizabeth, 7, until they left him. Now, authorities say he killed all three in their apartment while they slept.
Tynese Bryant was Barton's next door neighbor. Her son Melvin used to baby-sit for Matthew and Michelle, and she may have known the family better than most. She paints a poetic picture of man who loved his children, was deeply involved with their lives and was always first to say hello.
"He was a really friendly guy, always saying something funny, he was always joking all the time," Bryant says.
But Barton's life appears to have been full of conflicting images. While living a seemingly ideal suburban life, a farewell note read by police Friday tells of a troubled man behind the mask.
"I have been dying since October," Henry County police chief Jimmy Mercer read from the note. "I wake up at night so afraid, so terrified, that I couldn't be that afraid while awake."
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Authorities are slowly piecing together clues to Mark Barton's personality, trying to figure out why he went on the worst mass murder rampage in Atlanta's history.
Barton was tall, 6 feet 4 inches, and was known as a quiet, churchgoing man. He even appeared polite until the last few seconds before the rampage began.
"The only thing he said, while he was coming out or going in...was, 'I hope this doesn't ruin your trading day,'" recalls one surviving eyewitness.
A native of South Carolina, Barton had lived in the Atlanta suburb of Stockbridge for approximately one year, renting a neatly kept home in a modestly priced neighborhood.
He worked as a chemist, until he made a career shift and became a day trader. He reportedly lost $80,000 through the intense and risky investment technique and was having financial troubles.
Barton was also the prime suspect in the 1993 bludgeoning deaths of his first wife, Debra Spivey Barton, and mother-in-law Eloise Powell Spivey. He refused to take a polygraph test and no charges were filed. At their funeral, he stood near the hearse, even though he'd taken out a $600,000 life insurance policy on Debra two weeks before the murders.
Neighbor children recalled Barton as a man who was active in the Boy Scouts. One child said Barton's son said his father was "pretty nice" and would get him anything he wanted.
Other neighbors had their doubts, though. Marsha Jean DeFreese says Barton was a scoutmaster of her grandson's troop. But, she says he "looked odd," and she thought something was weird about him.