LITTLE ROCK, Ark. (AP) — A 5-year-old boy with developmental disabilities was found dead inside a daycare van where police said he'd been left all day in the sweltering heat, and an Arkansas agency launched an investigation Tuesday into why a vehicle alarm system and other safeguards didn't prevent the tragedy.

The Arkansas Department of Human Services identified the boy as Christopher Gardner. West Memphis police said he was picked up by the day care at 6:40 a.m. Monday but was never taken inside Ascent Children's Health Services, which serves children with developmental disabilities.

West Memphis is directly across the Mississippi River from Memphis, Tennessee.

"There are simply no words to express the overwhelming sadness we feel at the death of this child," Ascent Children's Health Services said in a statement. "We are heartbroken and our thoughts and prayers go out to the family."

The state agency said all child care services in Arkansas must follow certain safety requirements, including installing approved child safety alarm devices in vehicles used to transport more than seven passengers. According to the statement, the alarm system has to be installed in such a way that the driver is forced to walk to the back of the vehicle to reach a switch that deactivates the alarm.

The department said a Medicaid contract monitor inspected the day care van in February and the alarm system was deemed to be in working order. The agency and the Medicaid contract monitor were investigating the incident.

Department spokeswoman Brandi Hinkle said the facility had previously been "highly compliant."

Hinkle said the Arkansas Department of Health is closing the facility for the rest of the week due to a shigella outbreak, which can cause diarrhea and fever.

Police told Memphis, Tennessee, television station WMC that the boy was found dead, still strapped in a booster seat, more than eight hours later when staff members prepared to load the van for children to go home.

The boy's cause of death hasn't been released but the heat index neared 100 degrees Monday afternoon in West Memphis.

According to the television station, Christopher's family members said the child had undergone two heart surgeries and was at the day care for developmental disabilities.

Police would not say if charges would be filed in connection to the child's death.

Ascent Children's Health Services has nine other locations in Arkansas, including North Little Rock, Jonesboro and Benton. The company's website says Arkansas state Rep. Dan Sullivan has been the CEO of Ascent since 2004.

Sullivan didn't immediately respond to a message from The Associated Press.

The company's website describes the responsibilities of a van driver as being responsible for signing patients into the clinic for the day and that they are taken to their treatment rooms.

It says the van driver should complete a van checklist of the vehicle's condition each morning and afternoon before leaving the clinic. A third person, who is not a rider in the van, inspects the vehicle to ensure that children have not been left behind when the vehicle is returned to the clinic at the end of the day.

According to KidsandCars.org, there have been over 800 child heatstroke deaths involving vehicles since 1990 in the U.S. The organization said about 7 percent of those fatalities were the result of a childcare worker leaving the child in a vehicle.

KidsandCars founder Janette Fennell said that protocol for childcare workers transporting children usually involves someone picking up the child, checking them in to a facility and then taking that checklist to a manager, who also conducts an inspection to ensure all the kids are present.