Bill Romer, the landlord of Devlin's suburban St. Louis apartment, said on "Good Morning America Weekend Edition" Sunday that he never suspected anything was amiss. Romer said that for a man who was allegedly holding a boy against his will, Devlin aroused no suspicions.
"It's strange, because frankly he's one of my best tenants," Romer said. "He was a very pleasant, kind of low-key, regular guy."
Kidnapped at age 11, Hornbeck lived openly with Devlin at his apartment for more than four years. Devlin didn't even make an effort to conceal the apartment or what was going on inside.
"From what I could see, there were no curtains on the bedroom windows ... so it wasn't like he was trying to hide anything," Romer said.
Romer recalled Devlin referring to Hornbeck as his son.
"He told me on more than one occasion that it was his son that lived with him," he said. "I had nothing to lead me to believe anything was wrong with the situation."
Co-workers in 'Absolute Shock'
Devlin worked two jobs in St. Louis, one as a manager at an Imo's Pizza and another at a funeral home where he answered phone calls.
Both employers told ABC News that they had noticed nothing abnormal about Devlin.
Mike Prosperi, the owner of the Imo's Pizza, said he and his other employees were in "absolute shock" when they found out about the allegations against Devlin.
"Everybody who's been involved with Mike just can't believe it," Prosperi said.
Prosperi talked with Devlin's brother, Jamie, and said the suspect's family appears to be in a similar state of shock.
"When I talked to Jamie, there were one-word answers," Prosperi said. "He said, 'He's my brother. It's our family. ... We're lost.'"
Why Didn't Hornbeck Escape?
As details about Devlin's life with Hornbeck are revealed, many are wondering why the boy didn't seem to make an effort to escape.
While living with Devlin, Hornbeck called himself Shawn Devlin and had his own group of friends.
"He was a pretty nice kid, and we just clicked on so much stuff like video games," said David Douglas, who knew Hornbeck as Devlin's son.
Those friends even asked him directly if he was Hornbeck, but he never answered.
"No response," friend Kelly Douglas said. "He didn't look sad, or get up and walk out of the room, anything that would lead to us believing that he was actually Shawn Hornbeck."
Forensic psychiatrist Dr. Keith Ablow said Stockholm Syndrome, a psychological condition in which detained people exhibit loyalty to people holding them, likely played a part in Hornbeck's failure to attempt to flee from Devlin.
"If somebody has the power of life and death over you, that's a very good guy to feel aligned with, and so the mind does this," Ablow said. "It tells people, look, I'm on his team because he has the power of life and death over me."
Asked what Hornbeck's carefree demeanor at a Saturday press conference indicates about his mental state, Ablow said the boy has likely not come to terms with his disappearance and rescue yet.
"What you see is, you see an absence of the reactions that we might anticipate. There's no great rage. There's no terrible sadness coming forth," he said. "That means the mind has compartmentalized his plight, which is what the mind does."
This piece was compiled from reports and interviews that aired on "Good Morning America Weekend Edition."