Arthur Mann, the suspect in the fatal CNN Center shooting, is a registered sex offender in Florida

Ann O'Neill:

CeCe and Toon -- those are the nicknames kids in Clara Lee Riddles' and Arthur Lawrence Mann's neighborhood gave the doting couple.

Together for two years, they seemed in love. Mann, 39, hung out and talked basketball with neighborhood boys. Riddles, 22, was a big-sister type, always doling out advice. But two weeks ago, the couple broke up.

"That was his girl, man. That was his everything," said 18-year-old neighbor Joseph Brown.

Mann didn't seem angry. "I was talking to Toon three days ago. Everything was fine."

But all was not fine. Police say Mann walked into the CNN Center in downtown Atlanta and fatally shot Riddles on Tuesday, causing a flood of visitors in the CNN complex to scatter.

A witness described seeing Mann drag Riddles by her hair down an escalator from the lobby of the Omni Hotel, where she worked.

At the bottom of the escalator, just feet from an entrance to CNN.com, Mann shot Riddles three times -- in her shoulder, torso and, at close range, in the head, police and a Fulton County medical examiner investigator said.

A Turner Broadcasting security officer shot him.

Riddles and Mann were rushed to Grady Memorial Hospital, where she died and he is now in stable condition following surgery.

Atlanta police spokesman Officer James Polite said Mann is being held in a detention unit of the hospital and has been formally charged with murder and aggravated battery.

Neighbors said they didn't see the violence coming.

"That's not Toon," Brown said. "That's not him, from what I've seen."

Mann didn't talk about his past -- the eight years he spent in prison in Florida where he is a registered sex offender.

Court records in Florida tell this story: In July 1992, he was convicted of third-degree murder and two counts of robbery with a gun and was sentenced to 10 years, according to Robby Cunningham, a Florida Department of Corrections spokesman.

Mann served five years of that sentence, violated his probation at least twice, was put back in prison and when he got out was charged and convicted in March 1999 of having sex with a minor 16 to 17 years old. For that conviction, he was sentenced and served three years, Cunningham confirmed.

After his probation ended in March 2004, Mann later moved to Georgia, and in October 2006, he was convicted of failing to register as a sex offender in the state.

Records show he registered eight days later, but Georgia did not verify that registration until about two weeks ago, on March 22 of this year, which is about the same time neighbors say he and Riddles broke up.

CNN Shooting Suspect Has Long Rap Sheet