He has previously admitted to stabbing her to death on April 7, 2016. But the defendant, who has been diagnosed with schizophrenia, was so mentally ill at the time that he didn't realise what he was doing was wrong, his lawyers intend to argue.
Prosecutors have said that despite the mental illness he knew the difference between right and wrong, and that the killing was instead spurred by jealousy and anger.
What Gurpreet Kaur's family didn't know at the time was that she hadn't been going to school for quite some time, according to lawyers. Instead, Akash would pick her up each day from the station where her mother dropped her off, prosecutors have said.
"From the very beginning, they were a beautiful couple. They got on so well," recalled Akash's landlord and roommate, Doreen Visesio-Wellsford, who testified via audio-video feed from Australia.
She recalled Gurpreet Kaur as "a lovely girl" whom everyone called Preeti. The young woman would be at the Manurewa house most weekdays, she said.
But Akash's interactions with her, as well as with his roommates, began to change in the weeks before Gurpreet Kaur's death, the landlord recalled.
"I started noticing his whole attitude had changed - getting agitated, angry, asking the same questions repeatedly," Visesio-Wellsford recalled. "I started hearing a lot of arguments - not soft talking but quite loud."
Akash's increasingly strange behaviour included walking into her husband's room as he was sleeping and staring at him, she said.
Another roommate, Gaurav Kaushal, told police he also noticed changes in behaviour.
"Akash and Preeti used to fight a lot - maybe three or four days out of each week," Kaushal said. "Sometimes they would argue for three hours."
On April 6, one day before Kaur's death, Kaushal recalled his roommate acting especially bizarrely. Akash asked to use Kaushal's phone and then began scrolling through the photos on it.
"He then accused me of talking to Preeti," the witness told police.
That entire evening, Kaushal said the defendant made him feel uncomfortable - staring at him and repeatedly accusing him of talking to his girlfriend. After he went to bed that night, he awoke several times to find Akash in his room staring at him, he recalled.
"He was shouting at me and trying to pick a fight," Kaushal recalled. "He told me I hacked his Facebook account and was seeing her."
The argument only ended when their landlord intervened.
"What the hell is going on because you're acting very strange and different," Visesio-Wellsford said, explaining that she was starting to worry about the safety of her 6-year-old son. "This is not you."
Akash stormed out of the house and sped out of the driveway, she said.
In late 2015, Kaur's father had found out she was pregnant when Akash called him out of the blue. Gurcharan Singh said he had never heard of the defendant before and didn't know his daughter had been dating anyone.
"He said that he belongs to a good family and he has a good character but that Gurpreet wants to leave him," Singh testified through a Punjabi interpreter.
Throughout the testimony, Singh refused to say the defendant's name, instead referring to "the man sitting behind me" in the courtroom.
His testimony paused at one point as he put his head in his lap and wept. The defendant, meanwhile, looked into his own lap. The grieving father declined Crown prosecutor Gareth Kayes' suggestion that they take a short break.
"If we take a break, I'll still have this pain afterwards, sir," he said.
