During the trial, both sides accepted that Jutting had killed the two women. The verdict hinged on the issue of "diminished responsibility," whether his mental state at the time of the killings substantially impaired his responsibility.

On Tuesday McCoy said Jutting had "intentionally killed two young women and he did so in circumstances that were depraved, degenerate and debauched."

However, in a lengthy argument before the three judge Court of Appeal, McCoy said that during the trial four experts had given evidence in relation to Jutting's state of mind.

"All four agreed that at the material times, he was afflicted by and impaired with abnormal mental function," McCoy said. "Two of the experts found that his abnormal mental functioning constituted psychiatric disorders," he added.

Jutting's lawyers argued that he suffered from a debilitating combination of mental problems -- alcohol and cocaine addiction, narcissistic personality disorder and sexual sadism disorder.

McCoy said under law the test for diminished responsibility should be whether Jutting had "abnormal mental functioning" as a result of his mental problems. However, he said Judge Michael Stuart-Moore instructed the jury to impose a stricter guideline of whether the defendant had an actual medical disorder, as defined by the Diagnostic and Statistical Manual of Mental Disorders, a widely accepted standard published by the American Psychiatric Association.

He gave the example of a person having 70% of the symptoms of a mental disorder still being of abnormal mind, even if they could not be officially diagnosed, something he said witness testimony in the original trial supported.

"(Stuart-Moore) has narrowed down and therefore taken away from the jury the proper consideration of what is an abnormality of mind," McCoy said. "All four medical experts ... found that the applicant was suffering from an abnormality of mind because he had impaired mental functioning."

"(He) has wrongly conflated the psychiatric diagnosis of disorder with the definition of abnormality of mind."

Two murders in six days

On October 27, 2014, Jutting killed 23-year-old Ningsih after keeping her captive in his flat for three days. He tortured and degraded her, filming the acts on his iPhone, before slashing her throat in the shower.

Three days later, on November 1, with Ningsih's body in a suitcase on his balcony, Jutting killed 26-year-old Mujiasih after she wouldn't stop calling for help, minutes after entering his apartment.

Over the course of the six days in his apartment, Jutting made numerous videos on his phone, describing his plans for future torture and fears of being caught.

In handing down the original verdict, Stuart-Moore said Jutting had failed to show a "shred of remorse" and urged that "no one be fooled by (his) superficial charm."