Sean Laurence Waygood was serving 20 years for his role in a murder and two shootings that featured in the TV show Underbelly: Badness when he died from metastatic colourectal cancer in April last year.

Waygood, who lived among the millionaires in the Newcastle beachside suburb of Merewether, received a 50 per cent discount on his sentence for assisting authorities.

He was classified as an extremely dangerous and was imprisoned in the High Risk Management Unit - known as Supermax - at Goulburn jail.

At an inquest into his death on Friday, Waygood's mother Evelyn Waygood said her son's diagnosis and treatment were "neglected" and "delayed" because of his high risk status.

Mrs Waygood told State Coroner Michael Barnes her son was a "polite" man who never complained, a legacy of his commando training during his five years in the army.

"I still have no idea why he would have been a high risk prisoner," Mrs Waygood said.

"He was held with the 30 worst criminals in the state and I know what they've done - I've read about it - and I know he wasn't one of the 30 worst criminals in the state."

In 2009, Waygood was convicted for his role in the abduction and murder of convicted drug dealer and police informant Terry Falconer in 2001.

He wore a suit and carried a police ID when he and two associates posed as federal officers to lure Falconer out of a Sydney smash repair business where he was on day release from jail.

They drove Falconer to a property at Turramurra, drugged him, put him in a tool box and drove him to a property at Girvan, south-west of Bulahdelah. Falconer died during the journey.

Falconer was strung up and dismembered before his body parts were disposed of.

Some of his limbs were found floating in the Hastings River near Wauchope several months after his disappearance.

Waygood eventually rolled over and turned Crown witness.

Less than a year after he was sentenced to a non-parole period of 15 years in May 2010, he experienced bouts of severe abdominal pain.

Medical staff misdiagnosed him with renal colic or gastroenteritis and gave him a fibre supplement and paracetamol.

Corrective Services and Justice Health staff refused to take him to the closest hospital at Goulburn, because inmates of his classification require an entire ward to be closed off and four armed guards stationed 24 hours a day.

Instead, arrangements were made to take him to the Long Bay prison hospital. However, en route his condition deteriorated and he was taken to Goulburn with acute bowel obstruction.

He was subsequently diagnosed with colourectal cancer, which had spread to his liver. He underwent surgery, chemotherapy and ultimately palliative care in the secure ward of the Prince of Wales Hospital in Sydney.

Mrs Waygood said her son's cancer could have been cured had he been diagnosed and treated earlier.

"I have no interest in blaming anyone, my intention is to find some form of justice for my son's unnecessary suffering," she said.

The inquest heard prison authorities have to balance inmates' health with public safety, and moving extreme high risk prisoners causes major logistical problems.

Eminent oncologist  Richard Fox conducted a review of Waygood's medical history. He told the inquest the 43-year-old had experienced "excellent medical treatment".

"The diagnosis could have been made one to two weeks earlier but it would not have made any difference to the outcome of the metastatic disease," Professor Fox said.

Professor Fox described as "bizarre" and "a biological impossibility" Mrs Waygood's claim that the cancer that spread to his lungs was caused by the spilling of cancer cells into his bloodstream during surgery.

Mrs Waygood said her son told her the surgeon admitted this after the operation.

However, the inquest heard there was no record of this in the medical records.

"I can say absolutely no reason for Sean in his condition, and it would be totally out of character, to completely fabricate something like this," Mrs Waygood said.

The inquest continues.