(CNN) -- That 9-year-old Minnesota boy who slipped through security and hopped a flight to Las Vegas is no stranger to child protection investigators, who say he has a history of sneaking into a water park and was recently arrested after allegedly stealing a car, according to an e-mail obtained by the Minneapolis Star Tribune.
And it turns out that his mother works at the airport where he began his journey, a source close to the situation said.
The boy's father told CNN affiliate WCCO that his son has had issues in the past.
"I don't have an angel, OK. I have a 9-year-old," he said. "To me, he's got a behavioral problem."
The father, who WCCO did not identify, said the family has been unsuccessfully trying to get help for his son for years.
The Minneapolis Star Tribune reported that Janine Moore, area director of the Hennepin County Human Services and Public Health Department, wrote in an e-mail to agency administrators and County Board members of the boy's "pattern of behavior," which has included hanging out at a Bloomington, Minnesota, water park and blending in with a large family to slip through without paying.
She describes him as a "challenging" child, according to the Star Tribune.
The newspaper reported that there is an investigation into whether the boy's mother, who works at Minneapolis-St. Paul International Airport, helped him fly to Las Vegas. The newspaper did not report who was conducting that investigation.
The boy's father told WCCO that his wife reported their son missing on Thursday morning -- a day after they last saw him, leaving the house to take out the trash.
"We're not bad parents. We didn't think nothin' of it," the father said. "We thought he was at his friend's house."
The father said he never expected his son would take the light rail from their North Minneapolis neighborhood to the airport and sneak onto an airplane.
"I don't understand," he said. "You've got so (many) security checks at these airports. How can you let a 9-year-old sneak past security, get on the plane, without anyone stopping him, questioning him or anything?"
Authorities have been trying to figure out how the child was able to slip past security and airline gate agents and board Delta Flight 1651 without detection.
The boy went through security with other passengers, the Transportation Security Administration said in a statement Sunday, but officials were still trying to figure out how he did it -- and how he then got on the flight Thursday.
Patrick Hogan, a spokesman for the airport, said that surveillance video shows the boy briefly talking to a Delta gate agent before the flight.
A short while later, the video shows that the agent became "distracted," and that's when the boy was able to sneak through and board the plane, he said.
Hogan said the crew "became suspicious of the child's circumstances" during the flight. Crew members got in touch with authorities in Las Vegas and turned the boy over to Child Protective Services, Hogan said in a statement.
The boy, who remained in Nevada, will be returned to Minneapolis because that is "where issues will be addressed," a source with knowledge of the situation told CNN. It was unclear when he would return to Minnesota.
The agency did not immediately return a CNN telephone message Tuesday seeking comment on the Star Tribune report.
According to the Star Tribune, Moore said child protective workers have investigated the boy's family life four times.
"The reports have been inconsistent and there have been no injuries to the child; however, there is a pattern of behavior," the newspaper quoted her as saying in the e-mail.
The newspaper said Moore wrote that the boy was arrested two weeks ago after allegedly stealing a car. The e-mail didn't indicate whether the boy was the driver of the car or a passenger, the newspaper reported.
The newspaper also said Moore wrote that the boy has alleged that his mother has held a knife to his throat and that she was "stabbed and died."
"Typically, staff can tell if a child is lying, but with this child, they are unsure what is going on," the newspaper quoted the e-mail as reading.
Delta on Monday said it was reviewing surveillance video. Flight crew members alerted authorities to the boy.
CNN's Bill Kirkos contributed to this report.