Convicted murderer Sainey Marong says he was insane at time of killing.

al-Misri gives insanity as a legal defence (top of page 584). This was also used by Ishrat “Mike” Malik during the trial for the Ranui double honour killings where he slaughtered his wife and daughter halal style after they met with an Anglican priest and his wife for lunch.

Sainey Marong says his murder trial conviction was an injustice as he had untreated diabetes and was insane when he killed Christchurch sex worker Renee Duckmanton.

Marong, an Ilam butcher, was found guilty by a jury of murdering 22-year-old Duckmanton in May 2016, in what Justice Cameron Mander called a “particularly callous and cruel” way.

He strangled her after they had sex, then burned her body, which was found on a roadside near Rakaia the next day.

Marong, who was jailed for life with a minimum non-parole term of 18 years in April, told the Court of Appeal that the jury was not told he was behaving oddly when police pulled him over in his car, but his behaviour was not unusual for a mentally impaired person.

Marong said the Crown had no legal authority to prosecute him according to the Criminal Procedures (Mentally Impaired Persons) Act.

This meant he was unable to communicate properly with his lawyer, and the Act said if he had a communication deficit, knowledge, understanding or comprehension problems for conducting a defence, that amounted to a significant partial impairment, he said.

Marong was diagnosed with diabetes after his arrest, but his medical records were misrepresented at the trial, and his worsening kidney function and other problems in prison were not disclosed to the jury, he said.

Justice Forrest Miller said the Crown had two expert witnesses at Marong’s trial who were both very clear that Marong was not insane. They said untreated diabetes was capable of causing a disease of the mind but that was not the case for Marong.

Mark Lillico, representing the Crown, said at the trial Justice Mander had no hesitation in allowing the defence theory that it was an insulin deficiency that led to the murder, but all the expert evidence said it did not reach that threshold.

An amicus curiae (a helper to the court), Fiona Guy-Kidd, said Marong was found fit to stand trial early on.

He was diagnosed with an adjustment disorder with a depressed mood after he was imprisoned, but it was not relevant to his mental state at the time of the homicide. The evidence at the trial was that Marong was trying to silence Duckmanton.

Marong said the diagnosis after the offending was not relevant, and the jury should have said he was not guilty by reason of insanity.

Justice Miller said they were reserving their decision, which would be delivered within a few weeks.

Convicted murderer Sainey Marong says he was insane at time of killing