Families of Rayshaun Carr and Jaylen Clark Close, who had been involved in a police chase, learned of their deaths via Facebook

The deaths of two Indigenous teenagers whose bodies were discovered in the wreck of a stolen car on the side of the Gore Highway last year will be investigated by the Queensland coroner, after a 15-month-long campaign from their families.

The families of Rayshaun Carr, 17, and Jaylen Clark Close, 16, learned of their deaths through Facebook, more than 24 hours after the crash site was found. Only one person, one of Jaylen’s aunts, was informed directly by police.

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The Kamilaroi families say the lack of information, as well as suspicions about events leading up to their deaths, prompted them to write to the coroner in May last year and request an inquest. On Monday their request was granted, with a pre-inquest hearing set down for 26 August.

The crash was discovered about midday on 21 April 2018, down an embankment at the Wyaga Creek rest stop 66km north of Goondiwindi.

The teenagers were last seen by their friends leaving a house in Toowoomba late on the evening of 20 April in a green SSV commodore bound for Moree in New South Wales. The boys often stayed with family in Moree and Toowoomba.

The car had been stolen from the Sunshine Coast earlier that day, before being passed on to Rayshaun and Jaylen. They had been followed by police coming down from Brisbane. In a Facebook message to a cousin at 1.35pm, Rayshaun said he was in an SSV Storm “getting a chase … Cops are chasing me.”

Staff at the 24-hour petrol station on the Gore Highway at Captains Mountain, about 100km into the 349km drive from Toowoomba to Moree, saw a green SSV Commodore pulling away from the bowser shortly after midnight. It was followed at high speed by a black car, driving “like lightning”.

It passed a truck about 1am, reaching speeds of 167km/h and was not seen again until just after midday, when two farmers spotted the car on its roof at the rest stop.

Chris Martial, the acting inspector of the Queensland Fire and Emergency Services in Goondiwindi, told reporters at the scene that passersby would “have to be really looking to see the vehicle from the highway”. A police officer at the scene told reporters the car was “extensively damaged”.

Rayshaun was found in the car, Jaylen lying some distance away. A preliminary autopsy report for Rayshaun, seen by Guardian Australia, lists his cause of death as multiple injuries caused by a motor vehicle collision.

The following afternoon, NSW police visited Jaylen’s aunt in Moree and told her what had happened. Rayshaun’s aunt, who lived next door, heard the news and put it on Facebook. It was the first most close family members heard of the deaths.

A family spokeswoman, Melissa Carr, said that failure to properly notify next of kin set the tone for the police investigation of the crash, which included a delay in releasing their bodies and a lack of clear communication from police.

Neither family received formal notification of the boys’ deaths from Queensland police, who were investigating the crash. Instead they were identified from fingerprints. Carr spoke with investigating officers, and has had regular communication with the coroners’ court.

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They have accused police, who they allege harassed the boys before their deaths, of harassing family members in the months that followed. A statement authorised by both families states there are questions to answer over actions taken by police before the crash and during their investigation.

Carr, who is Rayshaun’s sister, said that conflict with police had exacerbated the grief of both families, describing the pressure they had been placed under as “an epidemic plaguing Aboriginal people in every state”.

“Every day is excruciating, agonising pain,” she said.

Both Queensland and NSW police told Guardian Australia they had not received a formal complaint from the families of either boy. The coronial report was completed by Queensland police, and NSW police said it supported the matter going to inquest.