Missing boy's first words for police

• Police say the missing 13-year-old thanked officers after they found him


• He was inside a hidden compartment, behind the linen closet, police say


• Police arrest boy's father and stepmother on false imprisonment, other charges


• The boy contacted his mother by phone, helping officers find him, police say

(CNN) -- A missing 13-year-old boy escaped from a hidden compartment in a Georgia home, crawling through a narrow opening behind the shelves of a linen closet to reach police.

The first thing he told officers, police said Monday, was "thank you."

"We told him who we were and we told him that we were here to help him," Clayton County Police Sgt. Joanne Southerland told reporters. "After minutes of talking with him, he was able to come out."

Before his rescue last week from an Atlanta-area home, the boy had been physically assaulted that day, Clayton County Police Chief Gregory Porter said.

See boy's emotional reunion with mom

The boy's mother told police he had been missing for four years. Porter told reporters Monday that investigators are still looking into the case. He declined to provide specific details, saying he didn't want to jeopardize the investigation.

"The point today is that the child is safe. ... There are a lot of unanswered questions at this point," he said.

The boy's father, 37-year-old Gregory Jean, and stepmother, 42-year-old Samantha Joy Davis, were arrested and charged with false imprisonment, cruelty to children and obstruction, Porter said. A judge denied them bond at a court appearance Sunday, CNN affiliate WSB reported. Three teenagers who were living in the home were also arrested, Porter said.

The boy was reunited Saturday morning with his mother, who lives out of state, police said over the weekend.

The hidden compartment where the boy was found, police said, was an area filled with wooden beams and insulation between the garage and attic of the home in Jonesboro, Georgia.

"It was an area where no person should be living or held. ... No one should have been in that area where we found the victim," Porter said.

Police said it was unclear exactly how long the boy had been inside the compartment. He also shared a bedroom in the house, Southerland said.

The boy's father and stepmother didn't do anything to physically stop police from searching the house, she said, but "there was a lot of deception."

"They denied knowing the child existed, denied knowing the child was in the residence," Southerland told reporters. "They had no idea who the child was or why we were there."

Police said they first went to the home in Jonesboro on Friday night after the boy's mother contacted them. On the first visit, they didn't find him. Then his mother called 911 again, this time with more information provided by her son.

Southerland said police returned to the home, determined to find the boy. While police were at the house, the boy was able to communicate with his mother and give more detailed information about his whereabouts. That, she said, is how investigators found him.

"When we get a call like that....we won't leave until we make sure that any child is safe," Southerland said. "And that's what we did. ... It's just a reminder that we never know what happens behind closed doors. And we have to take every call seriously."

CNN's Ralph Ellis, Jason Hanna and Chandler Friedman contributed to this report.