Top End Health mental health and drugs manager, Richard Campion, was thanked by his superiors for his “contribution” to the agency and congratulated on his new job in Victoria two weeks before an inquest into the deaths of three children who were known to sniff petrol heard he did not understand the law and guidelines around treatment plans.

In an email sent to staff just weeks before the inquest heard that the denial of treatment plans for the children breached NT Health guidelines, Top End Health chief operating officer Michelle McKay thanked Mr Campion “for his contribution” to the health agency over the years and celebrated his new job.

“I would like to congratulate Richard Campion on his appointment to the role of executive director of mental health with South West Healthcare in Victoria,” Ms McKay wrote.

“On behalf of TEHS, I want to thank Richard for his contribution over that time. Richard will leave at the end of October.”

Mr Campion, the mental health, alcohol and other drugs general manager, was employed at the health agency from 2012 and appointed general manager of Mental Health, Alcohol and Other Drugs with TEHS in February 2016.

The inquest by NT coroner Greg Cavanagh is investigating the deaths of three children in separate Arnhem Land communities, two from the results of petrol sniffing, and a third girl – who had also been sniffing petrol for five years – from suicide months after she was kicked out of rehabilitation. It heard three government agencies, Territory Families, the Education Department and NT Health admitted serious mistakes and failings.

Mr Cavangh heard NT Health guidelines were breached when for all three children – a 12-year-old boy, a 13-year-old boy and a 17-year-old girl -not being given treatment plans and Mr Campion admitted they all should have had their cases referred to the chief health officer.

This included a treatment plan being denied to a then 11-year-old boy known as Master W, after he was expelled from BushMob.

This boy latter died from petrol sniffing, aged 12-years-old.

Mr Campion told the inquest that despite assessors knowing Master W was at “risk of severe harm”, his case was not referred to the CHO.

He said Ms B, the 17-year-old, should have “well and truly” had her case referred to the CHO more than four years prior to her death.

“It appears there was some unfortunate human error,” he told the inquiry.

Mr Campion agreed with Counsel assisting the coroner Kelvin Currie that he did not “appear to have understood the law and guidelines in relation to these sorts of matters”.

South West Healthcare is a healthcare service in the Victorian regions of Warrnambool, Corangamite, Glenelg, Moyne and Southern Grampians shires.

They were contacted for a comment but did not respond by deadline.

Mr Cavanagh was to hear final submissions on Monday before handing down his findings at a later dare.