Two lovers who committed the "heartless and brutal killing" of one of their spouses will spend at least 17 years behind bars.

Amandeep Kaur, 32, and Gurjinder Singh, 27, were found guilty of the murder of Kaur's husband, 35-year-old Davender Singh, who had his throat slit as he sat in his car on a South Auckland road on August 7, 2014.

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The victim's neck was so deeply severed a pathologist classed it as "partial decapitation".


The slaying left a 13-year-old boy without a father and a mother facing life in prison.

Davender Singh's mother, Sukhvinder Kaur, who lives in India, said the boy had been rocked by the horrific murder.

"He says he will never forgive his mum for what she's done and he misses his father terribly," Ms Kaur said.

"He only has me to hug now."Crown prosecutor Natalie Walker said the murder involved "a high level of brutality and callousness" featuring "calculated and lengthy planning" but Kaur's lawyer, John Anderson, argued it was rudimentary and crudely executed.

Justice Graham Lang sentenced each defendant to a mandatory term of life imprisonment and deemed them equally culpable.

"Although Gurjinder Singh may have been responsible for most of the physical acts, nevertheless the notes make it clear Ms Kaur was very much an instigator of the offending," he said.

He agreed with the Crown's assessment of the seriousness of the crime and rejected the view of defence lawyers who believed the killers should receive a minimum period of 12 and a half years in jail.

The deliberate planning, which occurred over several weeks, and the 13 knife wounds to the victim were enough to persuade Justice Lang to adopt a higher non-parole period.

The defendants, who worked at Sistema Plastics in Penrose together, had an affair which lasted several months, before Gurjinder Singh's wife discovered the betrayal through Facebook messages and subsequently informed Davender Singh.

Three weeks later he bled to death in his Honda Torneo on Norman Spencer Drive.

When the infidelity was uncovered, the pair plotted to kill the victim so they could be together.

They were unable to call or text anymore because of their spouses' increased scrutiny, so they resorted to secret handwritten notes.

Police found the notes - most of which were written by Kaur - at their workplace and in Gurjinder Singh's car.

Ms Walker said the messages showed the depth of the passion between the defendants and their commitment to the fatal plot.

But she said Kaur concocted or at least exaggerated stories of regular beatings she suffered at the hands of her husband, in a bid to get the support of Gurjinder Singh.

"How would you kill and then after how we would come [back] ... what do you have that we can use to kill?"

"There is a lot of police around there," another note said.

On the night of the murder, Gurjinder Singh followed Kaur and her husband after work and struck when they pulled over to talk - a hit that had been extensively planned, Justice Lang said.

Though it was unclear who caused the fatal wound, the judge said it did not matter.

However, he said the evidence pointed to Gurjinder Singh cutting the victim's throat while Kaur held her husband in his seat.

A friend of Kaur and the victim, who did not want to be named, said she had known the couple for the past five years and described Davender Singh as "a loving person with a very caring nature".

"I spent time with Amandeep, supporting her until she was arrested, not thinking she would be responsible for killing her own husband," she said.

"Such huge disrespect has been shown to Davender, his family and our culture as a whole."