In a culture where teenagers gladly share the most intimate details of their blossoming lives, 19-year-old Geddy Kramer was a cipher.

He had no Facebook page, no Twitter account. In his high school yearbook, former classmates say, he appeared exactly once: in his senior-class photo.

It’s almost as if he never existed.

On Tuesday, however, Kramer finally left a mark: Just before 6 a.m., dressed in black and carrying a shotgun, he walked into the FedEx distribution center where he worked in Kennesaw. He quickly shot six other FedEx employees, then turned the shotgun on himself.

Kramer’s apparent suicide brought a mystifying end to a burst of workplace violence, leaving behind few clues about the forces that motivated his attack.

“The only thing I can say is the last time I saw him, which was a couple of months ago, he was a happy, joking fellow – a typical 19-year-old kid,” his grandmother, Betty Kramer, said by telephone from Florida. “This is just totally unbelievable to us.”

“We’re dealing with a whole lot here right now,” Kramer’s father, Scott, said in a brief interview. “We’re dealing with our own loss and wishing the best to everyone who was affected.”

In a statement issued through the police, Scott Kramer offered no reasons for the shooting. But he said: “We make no excuses for his actions and are shocked and devastated by them. There really are no words at a time like this.”

People who knew Geddy Kramer described him as quiet, respectful and polite. In the Acworth subdivision where Kramer lived with his father and younger brother, a neighbor said she often saw him mowing the lawn or walking the dogs.

“He’s a sweet kid,” the neighbor said.

Kramer barely left an impression at North Cobb High School, where he was among the nearly 600 students who graduated in 2013. In interviews at the school Tuesday, more than a dozen current students said they couldn’t remember Kramer. Shown his yearbook photo, one student said he vaguely remembered Kramer – but didn’t know him by name.

Another 2013 graduate, however, described Kramer as a caring friend who helped others with personal problems.

“I don’t know what brought him to do what he did, because that is not the Geddy we all knew,” Desire’ Davis, who had known Kramer since 2008, said Tuesday.

Kramer’s family moved from Florida to Acworth in the early 2000s, according to property records. It was a family not unlike many others in the middle-class suburb 30 miles from downtown Atlanta: Kramer’s father works with computers, and his mother, Tracy, is a registered nurse.

The parents divorced in 2012 after almost 21 years of marriage. Court records cite an “irretrievably broken” union but gave no details. A judge approved a joint-custody agreement that called for the children to live with their father 270 days of each year.

The Kramers filed for divorce the summer before Geddy’s senior year at North Cobb. The divorce became final just after Thanksgiving. Davis said Kramer seemed resigned to the end of his parents’ relationship.

“When he would talk to me about how they would argue a lot, he seemed pretty realistic, accepting, and understanding to the fact that they just didn’t get along,” Davis said. “Maybe the actual divorce just pushed him over, I’m not sure.”

It was unclear Tuesday when Geddy Kramer went to work at FedEx, a sprawling warehouse-like facility about six miles from his house. Co-workers interviewed outside the facility after the shooting had trouble remembering his name.

One of them, Liza Aiken, described Kramer, who loaded packages onto delivery trucks, as a good worker. He was quiet, Aiken said, although he sometimes joked with other employees.

But last Thursday, Aiken got annoyed with Kramer, who repeatedly shined the laser beam from a package scanning device into her eyes. When he wouldn’t stop, she reported his behavior to a manager.

“I don’t know if that had anything to do with anything,” Aiken said. “I don’t know if he was even in the right mental state.”

One of the few indicators of Kramer’s state of mind appears, ironically, in a place where he shared nothing about himself: Facebook.

At 5:21 p.m. Monday, Kramer’s mother posted an old picture of Geddy to her page. In the photo, apparently taken in a restaurant, Geddy’s brown hair falls to his shoulders. His smile reveals a mouthful of braces.

His mother alluded to a more recent change in his countenance.

“No braces now,” Tracy Kramer wrote, “and (he) shaves his head.”

AJC staff writer Marcus Garner contributed to this story.