Braydon Worldon's body was discovered on River Road, Wantabadgery, in December 2018 by a passing motorist.

The young boy's death occurred a few hours after he had celebrated his birthday.

NSW Deputy State coroner Elaine Truscott opened proceedings at Wagga Courthouse on Tuesday.

Coronial advocate Brooke Notley made an opening statement detailing the lengths police had gone to try to uncover the person responsible.

She told the court that on December 18, Braydon and his stepfather Peter - better known as Toby - began work but later stopped due to the heat.

Ms Notley said Braydon then spent time with his mother, Crystal, and stepfather before some friends visited for an hour.

During that time, Braydon consumed some alcohol.

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"About 6.10pm, Toby and Braydon resumed worked on Sunnybrae property," she said.

"Once finished, Braydon went to the sheds behind the homesteads, [and] it was the last time he was seen alive."

Ms Notley said Mrs Worldon looked for her son but was not too worried when she could not find him as he would often hide away if he was angry.

"Braydon was angry as he had not wanted to work on the afternoon of his birthday," she said.

About 1am on December 19, a driver returning home came around a bend on River Road and spotted something ahead of him on River Road.

Ms Notley said the driver soon realised it was a body.

"He drove slowly past the person and could see blood, as a result, he stopped, checked for a pulse, which he was unable to find and contacted triple zero," she said.

"He waited until police and ambulances arrived."

Braydon was found in the clothes he was last seen in, with a smashed bottle and his cap near his body.

Ms Notley said it was "obvious" he had suffered significant trauma, and no items or evidence were found at the site that did not belong to Braydon.

Glass fragments and dark green paint flecks were removed from his clothing, which studies found to be consistent with a glass bottle and a green letterbox that had been found knocked down the following day.

Ms Notley explained that an autopsy of the body found the direct cause of death to be multiple injuries, including extensive skull and rib fractures.

She said experts believe he was hit by a medium to heavy rigid vehicle.

"Braydon was upright in the posture and facing away from the impact of the vehicle," Ms Notley said.

"Braydon did not have any injury patterns consistent with kneeling."

Ms Notley also said the injuries sustained were consistent with an estimated vehicle speed of 90 to 110 km/h.

She said the death had left a "catastrophic hole" in the lives of his loved ones.

Police have analysed CCTV, conducted a media campaign, interviewed suspects - all to find the answers, Ms Notley concluded.

Magistrate Truscott will spend the next few hours at the site where Braydon's body was found.

The inquest will resume at 2pm, where lead Detective Senior Constable Stan Wall will give evidence.

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