Richard Campion was previously the general manager of Top End Health Service's mental health alcohol and other drugs division.

He has now been appointed executive director of mental health with SWH.

The inquest is into the separate deaths of a 12-year-old boy, a 13-year-old boy and a 17-year-old girl.

Mr Campion tendered a 38-page statutory declaration to the inquest, which was released by the court to The Standard.

"I would like to at the outset recognise that better cross agency care and collaboration in all three of these cases would have delivered a better standard of care and treatment to these three young people," he said.

"I acknowledge the work that the multi-agency community and child safety management group is undertaking to address these deficits."

Mr Campion said the service had identified a number of opportunities for improvement through the review of the tragic cases and committed to making necessary changes in the ongoing management of assessment teams through a framework of safety and quality.

He said documentation in respect to referral and collaboration with other agencies appeared to be where the most improvement could be made.

SWH spokeswoman Suzan Morey issued a statement after Mr Campion's appointment was noted during the inquest.

"We believe it's premature to comment on this matter before findings and recommendations from the inquest have been released," she said.

It's understood Mr Campion was cross-examined about treatment plans for the deceased children.

It has been reported by a number of news sources that none of the children had treatment plans and health officials were not fully aware of their obligations.

Questions have been raised about the care provided by a number of government agencies.

Mr Campion was thanked by TEHS for his "contribution" to the agency and congratulated on his new job in Victoria two weeks before the inquest.

The youngest boy started sniffing aviation fuel when he was 11 and there was trouble finding him a placement in services which only catered for children when they reached 12.

Mr Campion acknowledged some information provided about the boy not sniffing petrol was inaccurate and a funding request had not properly been forwarded, which he said would "most likely" would have been approved.

It was alleged the boy had forced a five-year-old boy to sniff petrol.

The 17-year-old girl led a tragic life, involving allegations of sexual assault when she just 12, later a serious physical assault at the hands of a boyfriend with an axe or hammer and a number of incidents of self-harm before her death.

It was reported in her community at one stage people were sniffing petrol, paint and deodorant.

Mr Campion identified record keeping in relation to that case concerning communication with external stakeholders "could have been better".

She was known to sniff petrol over about four years.

The 13-year-old boy came to the attention of authorities after being captured on security camera footage getting fuel from a service station bowser.

At the time of his death he was known to have been sniffing petrol for more than two years.

Mr Campion worked at TEHS and the NT Department of Health since 2012 and was appointed general manager of the mental health, alcohol and other drugs service in February 2016.

NT coroner Greg Cavanagh is expected to hand down findings at a later date.

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