Ms Walker said the jury did not need to decide who partially decapitated Davender Singh.
"If you can't be sure who inflicted the fatal wound or held him down, that doesn't matter, provided they shared the intention to kill and that one inflicted the fatal blow and one assisted," she said.
The Crown told the jury it was most likely Gurjinder Singh had slashed the victim's throat while Kaur held her husband down.
But it was not just what happened inside the Honda Torneo on Norman Spencer Drive that was important, Mr Walker said.
The affair between the defendants, which lasted several months, was eventually uncovered by Gurjinder Singh's wife three weeks before the alleged murder.
Hundreds of text messages and calls between the pair ceased immediately and they resorted to exchanging handwritten notes while they worked as forklift drivers at Sistema plastics in Penrose.
Ms Walker said those notes, found by police, showed the couple's love for each other as well as how Kaur allegedly manipulated her co-accused.
"She seems to paint a picture of a jealous husband who was abusing her daily. She describes crying all night and being subjected to repeated beatings, and pleads with Gurjinder to save her," the prosecutor said.
"The Crown says these type of notes seem to be attempts to convince Gurjinder that Davender's violence against her must be stopped."
Flatmates and colleagues of Kaur had seen no signs her husband had abused her, she told the court.
Ms Walker said the notes over the three weeks before the victim's death also showed there had been previous plots to kill him in the preceding days.
Kaur had told her lover of various areas where she would regularly stop in the car to talk to her husband.
Initially it is alleged the plan was for Gurjinder Singh to find them there and launch the attack but after that proved unsuccessful they decided it best he follow them and wait for them to pull over.
Though scientific evidence from the body and inside the car did not point to a specific defendant being the principal party, Ms Walker said that should not trouble the jury.
"This is a case where the killing of Davender Singh could not have happened by one defendant alone," she said.
CCTV footage shows Gurjinder Singh leave the scene. Two minutes later, Kaur is pictured getting out of the car to phone for help.
"The reason for that?" Ms Walker said. "To give Mr Singh time to get away."
The trial continues.
