June 22, 2016 06:20 PM

Detectives in Louisiana believe that the 3-year-old siblings found unresponsive on Saturday in the stifling cab of their father’s truck may have used a footstool to access the pickup, becoming trapped as the vehicle’s internal temperature continued to rise, PEOPLE confirms.

A Bossier City Police Department spokesman tells PEOPLE investigators are still trying to determine how twins Oliver and Aria Orr managed to enter their father’s truck, and have been sharing their findings with prosecutors who are mulling potential criminal charges.

The spokesman claims detectives suspect the twins lugged a footstool over to the truck and climbed inside. The children closed the truck’s door and were unable to free themselves from the hot car.

PEOPLE has also learned that the children’s mother reached out to neighbors to help find the two 3-year-olds after they had gone missing. One of those neighbors located the brother and sister inside the truck at around 3 p.m.; both children were not conscious or moving, according to police.

“The children got into that truck by themselves,” the spokesman says. “That’s what we believe happened here.”

The truck was parked in the Orr family home’s driveway, according to investigators.

Autopsies on the Orr twins revealed their deaths were heat-related. No criminal charges have been filed against the children’s mother or their father, Travis Orr, who works as a deputy with the Bossier Parish Sheriff’s Office.

The twins’ deaths come just three weeks after Oliver was released from the hospital after suffering a near-fatal injury, according to police. The boy was in the hospital for over a week for treatment of unspecified injuries.

The police spokesman tells PEOPLE the children’s father has been placed on administrative leave.

“It was an unfortunate tragedy that he’s going to need some time to process,” the spokesman explains.

In a statement this week, the Bossier Parish Sheriff’s Office collectively expressed sadness over “the tragic loss suffered by the Orr family, and our hearts are heavy.”

The statement concludes: “This is a very difficult time, but it’s even more so, as they are part of our Bossier Sheriff’s Office Family. Please keep Deputy Travis Orr and his family in your thoughts and prayers.”

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