A year after the body of a Wisconsin toddler was found in a locked car trunk, the Polk County district attorney's office has ruled the boy's death a "tragic accident" and has closed the case without filing criminal charges, it announced Wednesday.

The body of 2-year-old Isaiah Theis was found July 17, 2013, a little more than 24 hours after he wandered from his home near Centuria, Wis., about 60 miles northeast of St. Paul. Preliminary autopsy results showed that Isaiah died from excessive heat.

Temperatures in Centuria rose to 91 degrees on July 16, 2013, and 92 the next day. Temperatures in the trunk would have been much higher.

"I didn't see any intent here on the part of anyone. I didn't see any recklessness," Polk County District Attorney Daniel Steffen said Wednesday, adding, "I think it's obviously every parent's nightmare."

Steffen said authorities took their time investigating the case and tried not to rush to judgment, conducting numerous forensic tests and re-creations of the events of the day the boy disappeared.

Isaiah vanished while playing with his 7-year-old brother. His disappearance set off a large-scale search in which thousands of people combed fields and forests and checked ponds.

Search teams passed the car, which they were told had been locked before Isaiah disappeared, numerous times, but the boy wasn't discovered in the trunk until the vehicle's owner, who had left it with Isaiah's father to repair, came to claim it. The car's keys were also in the trunk with Isaiah's body.

The finding shocked many and raised questions about how Isaiah got inside the trunk.

At first, Steffen himself was skeptical.

However, during a re-creation, the 2-year-old child of a deputy was able to climb into a trunk and shut it closed, Steffen said.

"It was quite surprising how easy it was," he said.

While the child was the same size as Isaiah, Isaiah was more familiar with cars because he spent so much time around his father, who was a mechanic, and the vehicles his father worked on, Steffen said.

Steffen said that he doesn't believe filing criminal charges is "going to do anybody any good," adding, "I think the parents have been punished enough, frankly."

The FBI, Wisconsin's Division of Criminal Investigation and the Wisconsin State Crime Laboratory assisted with the case.

Nicole Norfleet • 612-673-4495

Twitter: @stribnorfleet