Relatives say Harrell had always been overweight and slow in school, and had often been picked on, even by his two younger step-brothers.
A MySpace profile Harrell kept showed glimpses of someone who can't take it anymore, seemingly wanting revenge.
The song that topped Harrell's playlist was "Waking the Demon" by Bullet for My Valentine. In the song, a victim of bullying is transformed by blind rage and viciously attacks and kills his tormentor.
Was it a peek into the mind of someone who was about to snap -- or nothing more than average teenage angst?
It turns out police had been tipped off about Harrell's alleged interest in child pornography two months before Somer disappeared.
Lisa and Rod Buchannan knew Harrell through his stepfather, who was active in their church. In the summer of 2008, when Annis asked whether Harrell could move into an apartment complex with the Buchannans' daughter, Katie, and her fiance, the Buchannans agreed.
But the arrangement didn't last long.
"Things turned up missing" within a month or two, Rod Buchannan told ABC News' Chris Cuomo. Katie and her fiance said that one night they found their iPod in Harrell's car.
"Being that he was a family friend, they give him an option," Buchannan said. "Get your stuff, get out right now, middle of the night -- or we call the police and put you in jail."
The Buchannans say Harrell left -- but he left behind his computer.
That was a mistake. Buchannan's son knew a dark secret about what might be on Harrell's computer. He told his sister.
"So they decided to search the computer at that point," Rod Buchannan said. "And that's when they found -- I mean, it was right there on the desktop. There was no effort made whatsoever to hide the material."
The Buchannan siblings told their parents they had found child pornography on Harrell's computer -- a lot of it.
"Stuff that our children shouldn't have seen," Rod Buchannan said. "Should have never had to see."
Rod Buchannan took his wife and daughter to the police to turn over the computer. He said that Katie told police she feared that Harrell might have known some of the children in the pictures.
Harrell had plenty of access to kids. He babysat his sister's children. His sister ran a business selling toddler items out of her home. They lived in a neighborhood filled with young kids.
As it turned out, Katie Buchannan's fears were justified, authorities say. After Harrell's arrest, police said, they found his camera. It had more photos and a video on it of a 3-year-old child whom Harrell knew, they said.
After Harrell was arrested, Cuomo asked Somer Thompson's mother, Diena Thompson, about her feelings about the murder suspect. Did it help her understand how Harrell got to the point he allegedly did?
"No," Thompson said. "I don't feel sorry for him. You make choices in life. And all of us go through trials and tribulations. ... I have been through similar circumstances in my life, and I'm not killing, raping, stealing children.
"You make choices to do things different. Stop the cycle, end the abuse, don't do this."