Coroner finds Heather Bills' death wasn't an accident

When Heather Bills was rescued from a raging house fire in 2012 she was badly injured but was expected to live. 

Six weeks later when she suddenly died in Middlemore Hospital alarm bells started ringing. 

Nearly five years on a coroner has confirmed her cause of death was a "non-accidental overdose of insulin".

Who gave it to her remains a mystery but Chief Coroner Judge Deborah Marshall has shed some light on how it happened.

In her written findings, Judge Marshall stated while being treated in hospital Heather Bills was largely uncommunicative and often expressed a wish to die.

But Judge Marshall said because of her hand injuries "opening a vial and preparing an injection would have been beyond her abilities but she may have been able to inject insulin if it was given to her."

"...the overdose must have been administered by someone who had access to insulin and the secure NBC (National Burns Centre)".

The report also outlines why senior medical staff missed signs Mrs Bills was suffering a hyperglycaemic event. 

A nurse, who's been granted name suppression, claimed to have tested Mrs Bills blood sugar level and told doctors the result was normal.

But Judge Marshall found no evidence to support those results and said "Tragically, the reported 6.4 reading led the clinicians to discount hypoglycaemia as a possible cause of Mrs Bills' rapid decline".

"...if the hypoglycaemia had been recognised earlier... Mrs Bills would likely have survived."

As a result of the hospital's own investigation, a new electronic system for recording abnormal observations is being trialled and insulin is now stored in a secure drawer.

At the time of Mrs Bills death, police were called in to investigate, but no charges have been laid. 

Police say they'll now review the Coroner's findings and their own investigation but that will take some time.