An investigation is underway after the death of 3-year-old twins in Bossier City, Louisiana, just outside Shreveport.

Police said the twins, a boy and a girl identified as Oliver and Aria Orr, were found unresponsive in a pickup truck parked at their home.

>> Read more trending stories

"Neighbors tell police the children's mother, who was home at the time, had contacted them saying she was looking for the children," according to a statement from the Bossier City Police Department.

KALB reported that the mother, Alisha Orr, said she laid down before the twins got out of their home.

Neighbor Rhonda Matthews said Alisha Orr looked in the backyard, and when she found Aria in the car, she screamed. They then found Oliver in the back of the truck.

Police were called to the home after Matthews attempted CPR on both children to no avail.

The Shreveport Times reported that the father of the twins, Travis Orr, is a deputy with the Bossier Parish Sheriff's Office.

"We are saddened by the tragic loss suffered by the Orr family, and our hearts are heavy," Bossier Sheriff Julian Whittington said in a statement on Facebook. "This is a very difficult time, but it's even more so, as they are a part of our Bossier Sheriff's Office family. Please keep Deputy Travis Orr and his family in your thoughts and prayers."

Authorities said the twins may have been in the car for two or three hours.

Cause of death has yet to be determined, but Bossier City Public Information Officer Mark Natale said the deaths may be heat-related, according to preliminary autopsy results.

Natale said there were no signs of trauma to the children and the investigation will determine how the children got into the truck.