A 5-year-old Arizona boy found dead five days after vanishing from a campsite north of the Grand Canyon likely died from exposure, authorities said Tuesday.

The Coconino County Medical Examiner's Office in Flagstaff performed an autopsy on Jerold Joseph Williams a day after his body was found by a search crew off a forest service road.

The Colorado City child had wandered away from a campsite last Thursday in the Kaibab National Forest north of the Grand Canyon while chasing grasshoppers.

Jerold was with a group of about 20 people when he went missing about 12 miles south of Jacob Lake.

"He was found fully clothed with no obvious external injuries and there was no evidence of foul play indicated at the scene," county sheriff's spokesman Gerry Blair said in a statement.

"The weather had turned inclement early during the time he was missing" and the medical examiner's preliminary findings "appear to be accidental death due to environmental exposure," Blair added. "Based on the environmental conditions Jerold was exposed to, it is unlikely he survived the first night."

Blair said the boy's body was found around 4:30 p.m. Monday by a group of volunteer searchers from Colorado City.

The group was driving in a pickup truck along Forest Service Road 240 when they spotted a body on the ground around 15 to 20 feet off the road.

The body was found nearly 4 miles from the place the boy was last seen.

"Because Jerold was found close to the road and the road would have been a natural walking area for him compared to the very thick brush, it is believed that Jerold probably found his way to Forest Road 240 and followed it to Forest Road 241 in the direction away from the campsite and may have walked off into the forest to lay down to rest," Blair said.

Authorities said more than 1,000 people helped in the search over five days that covered about 21 square miles.

The search was aided by military helicopters equipped with night vision equipment, ground crews with dogs and ATVs, and numerous volunteers from Jerald's hometown.

On Monday, some volunteers walked shoulder-to-shoulder through thick vegetation in heavy rain in hopes of finding clues before the body was found.