The DNA evidence, which the Crown had earlier cited as a key part of its case in proving Anderson was guilty of the stabbing murdering his 5-months pregnant girlfriend Allira Green, was "quite wrong", Justice Lucy McCallum said.

The jury had initially been told that the evidence of four swabs, purportedly from the hands and fingernails of Anderson, had returned matches with the DNA of the Ms Green's two friends, Allira Holt and Louise Bodeker, who were present when Ms Green was stabbed to death in a Maroubra unit in the early hours of August 3, 2013.

The evidence supported the Crown's case that a struggle between Anderson and the three women had broken out before Ms Green was fatally stabbed.

But it was revealed on Tuesday that the swabs had been incorrectly attributed to Anderson by police, and were in fact the DNA swabs from Ms Holt and Ms Bodeker.

The mistake, which was revealed to the jury during the final day of the trial's evidence, arose after the forensics samples arrived unlabelled at the laboratory where they were tested.

Senior forensic biologist Ivana Sesardic told the jury she contacted police seeking clarification of the source of the DNA samples after the swabs arrived with "no information as to the donor or names attached."

Detective Senior Constable Ryan Morgan confirmed that the swabs belonged to the accused, Ms Sesardic said.

Although he could not recall the conversation, Detective Senior Constable Morgan accepted there had been an "obvious mistake" as there was "nothing in the police system that said [the swabs] were Anderson's".

In her closing argument Crown prosecutor Virginia Lydiard conceded that this DNA evidence "was flawed" but said the jury should have "no difficulty" in finding Anderson had stabbed Ms Green before fleeing the scene because separate evidence proved his DNA was on the handle of the knife.

While neither witness saw Anderson stab Ms Green, Ms Lydiard reminded the jury that Louise Bodeker had testified to seeing Anderson's right hand clenched over the knife after Ms Green had rushed at him with the weapon "pointed towards him."

Ms Lydiard said this supported the Crown's version of events: that when Anderson "gained control of the knife" he formed the intent to either kill Ms Green or cause her grievous bodily harm.

Ms Green's fatal injury - a single 15cm stab wound that pierced her heart - was evidence of the "deliberate nature of the stabbing," she said.

"If he had stabbed her in self defence you might think he would have stayed to help the mother of his child."

The Crown's case, although circumstantial, was supported by a number of pieces of evidence Ms Lydiard said, including the "dysfunctional relationship" between Anderson and Ms Green," the depth of Ms Green's stab wound, and that Anderson had fled the scene and changed his clothes.

Defence barrister Charles Waterstreet, who has argued Ms Green's death was an "unfortunate accident", is expected to present his closing arguments on Tuesday.