Detail by emerging detail, the Midtown lunch-hour killing of Brittney Fox Watts only grew more baffling -- and more deeply unsettling -- Monday.

Just as she was an unlikely victim -- a bubbly 26- year-old delighted with her life and only recently returned to her hometown -- the suspect was an unlikely killer: not only a security guard but the church-going son of a high-achieving family, including a mother who is an attorney versed in death-penalty law.

Nkosi Thandiwe, 22, of Atlanta, is charged with murder in Watts' death; he also faces two counts of aggravated assault in the shooting of two other women wounded in the same parking garage where Watts was gunned down Friday.

Monday, police beefed up security around the garage and the Proscenium building across the street, where both Watts and Thandiwe worked -- she for the advertising and marketing firm 22squared, and he for AlliedBarton Security Services.

Workers entering and leaving the high rise, located at the corner of Peachtree Street and 14th Street, were somber and a little scared.

“Everyone is kind of shaken up," said Crystal Andrews-Newell, 33. "He was a security guard. He’s supposed to take care of people.”

Nicole Pritchett, 39, said she had spoken several times to Thandiwe during the year that he had worked there.

“He asked me about my hair,” she said. “He seemed to be a nice guy.”

Police haven't yet offered a motive for the shootings, or determined whether the gunman targeted Watts or chose her at random. If the two were acquainted, though, it can only have been briefly: Watts had worked in the Proscenium building for only about a month.

Her murder made headlines as far away as Seattle and London.

"It is the randomness of it," said Dick Reed, a media analyst in Berkeley, Calif. After the initial shock, he said, it's the mystery, the unknowns, that hold people's interest.

“That helps sustain it ... People keep watching to see if more information is released.”

It wasn't just that the life of a bright and accomplished young woman was taken, media and criminology experts said, but that it happened at a  time and place not generally associated with deadly violence. During daylight hours, the area around Midtown's phalanx of skyscrapers is bustling with young up-and-comers clad in stylish suits and carefully-crafted ensembles.

“This is upscale living, young and upwardly mobile people, high-end shopping,” said Volkan Topalli, an associate professor of criminal justice at Georgia State University's Andrew Young School. “It’s a shocker.”

Watts and her husband, Brian, had only recently moved back to the Atlanta area from Tampa, where they had lived since 2008, and where she had also worked for 22squared.

Both graduates of Roswell High School and the University of Georgia, they had purchased a home in a desirable Decatur neighborhood, and Brittney had set about buying paint.

The petite Watts blogged regularly about her life, sharing with readers her love for her husband and for their dog, Willow, and her joy about  moving back home.

In one post, she described a day of fits and starts before writing: "I realized that I am not dying, my family is healthy, and happy, and when I have bad days/mornings, I realize my day is a dream compared to others who are suffering from much worse."

That glimpse into a charming and seemingly charmed existence -- full of the joys of traveling, flea market finds, photography and vintage bicycles -- is in keeping with the young woman others encountered.

“She was just a sweetheart, a beautiful young lady," said Natalie Gregory, a realtor who worked with the couple during the sale, representing the seller.

What little is known about Thandiwe only makes the crime more shocking. One of four siblings, he is the son of an engineer and an Atlanta attorney educated at elite West Coast universities.

In the late 1990s, the family was the subject of a brief item in the Atlanta Journal-Constitution that noted their shared love of running. Thandiwe's parents both are stalwarts in South Fulton Running Partners, which regularly contributes to charities.

Family members are also longtime members of Cascade United Methodist Church in southwest Atlanta. A church spokesman confirmed Monday that Nkosi Thandiwe was "rededicated" at the church in January.

He was hired a little less than a year ago, AlliedBarton Security Services confirmed Friday. The company said he passed a background screening conducted under the Georgia Bureau of Investigation’s security personnel clearance requirements.

Neither Watts' nor Thandiwe's families have commented publicly about the killing, and neither could be reached for comment Monday.

Meanwhile, the other women wounded in the attack continued their recoveries. Lauren Garcia,23, who was shot in the back, remains hospitalized. Tiffany Ferenczy, who was wounded in the leg, has been released from the hospital.

As police continue to put together the pieces, Watts' family and friends will gather Tuesday to remember a woman described in online blogs and tweets as "genuine" and "positive."

"She was smart and lovely and poised and fun and goofy," a friend blogged a day after her killing. "She lived in the present, and was truly appreciative of all life had to offer."

Reporter Christian Boone contributed to this report.