Justice Williams gave the jury the usual advice - to consider evidence carefully, ignore outside reports, and not allow any feelings of prejudice or sympathy to influence their deliberation.
He also acknowledged the tragic impact Ms Fan's death had on her and Preston's children. "They were caught up in a nightmare scenario not of their making and probably not fully understood."
The judge said he could imagine jurors felt sorry for Ms Fan - and he did too - but that didn't mean Preston was guilty.
Justice Williams said Preston was easily seen as a person of "eccentric character" who could come across as not very likeable.
That too, the jurors would have to ignore.
And the judge recalled the often caustic arguments that characterised Preston and Fan's relationship.
"Nasty things were said and done, including nasty things by Mr Preston."
But that too, the jurors would have to disregard.
"Whether you like Mr Preston or not is utterly irrelevant."
The Crown case is that Preston killed Ms Fan in a frenzied knife attack in the suburb of Miramar to gain sole custody of the couple's two children.
Preston denied this, and denied breaching a protection order Ms Fan had taken out against him.
On Friday, Crown prosecutor Grant Burston said Preston had "three windows of opportunities" to kill Ms Fan, whose body was found on her laundry floor with multiple stab wounds on the Sunday after her death.
Mr Burston alleged the 60-year-old had "targeted" Ms Fan's neck and face as she was stabbed 15 times.
He added the person who killed Ms Fan must have "really hated" her.
"He had finally had enough. He stabbed her 15 times in the neck with a carving knife and left the knife there," he said.
But defence lawyer Louise Sziranyi urged the jury to keep an open mind. She said there was no direct forensic evidence to suggest Preston killed his estranged wife.
Ms Sziranyi acknowledged the murder was a "tragic and horrific event" but said Preston was genuinely distressed when he realised his two children weren't picked up on the day of Ms Fan's death.
Justice Williams said if the jury found Preston guilty of murder, he'd "obviously" be guilty of breaching the protection order too.
Likewise, a murder acquittal would necessitate an acquittal on the other charge.
Justice Williams said there was no doubt the Crown case was circumstantial, with no direct evidence Preston was at the Brussels St house when Ms Fan was brutally killed.
"Rather, the Crown invites you to infer certain things."
These inferences included the idea Preston had a motive to kill his estranged wife.
Justice Williams said the defence also argued there was no way Preston had time on that Friday morning to visit Miramar, kill Ms Fan, and dispose of his blood-soaked clothes and other incriminating evidence in the window of time available to him.
He said another defence argument hinged on the suggestion the killing was not "personal" and Ms Fan's body was not defaced or mutilated.
The judge urged the jury to treat as irrelevant evidence of a religious note found at the crime scene.
Justice Williams said the Crown sought to weave together 12 different strands in its desire to persuade the jury to find Preston guilty.
These included allegations Ms Fan feared Preston would kill her, Preston's "motive", and his "telling and unusual statements" after her death.
The trial heard Fan told a police officer she was worried about Preston's reaction if she succeeded at getting custody of the couple's two children.
She allegedly asked her estranged husband in a text message in July 2013: "Are you going to kill me?"
The judge also recalled a conversation Preston had with a New Zealand Herald reporter when Preston uttered the words "Several weeks after I'd done it."
The defence said it was unreliable and incorrect to suggest Preston had a tendency to threaten and behave violently to Ms Fan.
In particular, the Crown said Preston had a tendency to "use knives" with Ms Fan, but the defence said this suggestion was "old and unbelievable."
Preston at times cited the possibility of a professional "hit" on Ms Fan, and pointed to her boyfriend and her uncle as possible suspects.
Justice Williams said the Crown generally discounted the chance of alternative perpetrators "and the defence did not seriously advance these options in cross-examination."
Although the defence pointed to evidence Ms Fan's uncle had lost money in a business venture Ms Fan was involved in, Justice Williams said the possibility of a professional "hit" on Ms Fan raised doubts.
"Would a hitman really use washing-up gloves and an old carving knife?" he said, paraphrasing the Crown argument.
In any case, the judge said it was not Preston's job to find a "plausible perpetrator" and the onus was on the Crown to prove his guilt.
Justice Williams said the Crown argued a "gradual shift in the power dynamic between the two" left Preston in the cold, culminating in Ms Fan's "complete independence" from Preston.
This, prosecutors argued, contributed to Preston snapping.
But the judge then reminded the jurors of defence arguments that the 1100-odd intercepted communications found nothing that implicated Preston.
In concluding remarks, the judge reminded the jury they were required to reach a unanimous verdict, and only much later, and in extreme circumstances, would a "majority verdict" of 11-1 be accepted.