Two lovers accused of plotting the bloody execution of one of their spouses have both been found guilty of murder.

Amandeep Kaur, 32, and Gurjinder Singh, 27, were held jointly responsible for slitting the throat of Kaur's husband, 35-year-old Davender Singh, as he sat in his car on a South Auckland road on August 7 last year.

After a second day of deliberation, the jury returned the guilty verdicts this afternoon in the High Court at Auckland.

The victim's neck was so deeply severed a pathologist classed it as "partial decapitation" and said blood would have sprayed from the wound.

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.

She informed Davender Singh.

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

The Crown said when the infidelities were uncovered by their respective partners, 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 the workplace and in Gurjinder Singh's car.

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

"Lali, if everything goes well today do not spare him, he made me suffer a lot really. I do not want to live with him. Love you," one read.

Crown prosecutor Natalie Walker said Kaur concocted or at least exaggerated a story 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 when he picked her up from work and struck when they pulled over to talk.

Though it was unclear who caused the fatal wound, Ms Walker said it did not matter because both were equally culpable.

However, she said it was most likely Gurjinder Singh wielded the knife while Kaur held her husband in his seat.

While giving evidence throughout the four and a half week trial, Kaur admitted there was a plan to kill but said the day before the murder she had withdrawn from it and reconciled with her husband.

Gurjinder Singh rejected the existence of such a plan and said he turned up at the scene after Kaur had stabbed Davender Singh to death, only taking away evidence when she threatened to blame him.

The jury rejected both versions of events.

There was no audible reaction from the dock or public gallery when the verdicts were handed down, but some in the gallery had faint smiles.

Justice Graham Lang convicted the pair of murder and gave them warnings under the three strikes law.