Ms Fan died after being stabbed multiple times with a kitchen knife in her home by a killer police believe was wearing a disguise. She wasn't found for two days. This week police revealed the crime scene was broken into about a month after the murder and a small card with a religious verse on it had been placed near a photo of Ms Fan.
Detective Senior Sergeant John van den Heuvel, the officer in charge of the case, said the investigation net was tightening on the killer.
"In these whodunit-type cases, we start with a very large suspect list, anyone and everyone. But as the investigation progresses, the suspect list narrows. Suspects obviously include people known to Mei.
"We're still keeping an open mind as to who may have done this. I can't be specific but, needless to say, our suspect list is now quite short."
In his first media interview, Mr Preston told the Herald that although he thought police "believed it was me", he was innocent and didn't deserve the scrutiny.
"I didn't do it, of course not. I have always maintained my innocence," he said. "Yeah, I'm a suspect but I've got pretty bloody rock-solid alibis. And also they've got no evidence. And that's the worst part it's not that they've got no evidence against me, it's that they've got no evidence."
He claimed his wife, who he met in China, had fled her homeland after becoming involved in a crooked financial scheme which had made her enemies.
Police want sightings of Michael Preston's car on the day of the murder.
Ms Fan was found the floor of her home in Miramar, Wellington, on Sunday, November 10. Police think the killer likely arrived at the house in disguise, slaughtered her with a 32cm knife left behind at the scene, then changed clothes and departed.
The disguise may have been a subtle one, Mr van den Heuvel said, but would likely have been enough to make the killer unrecognisable to the victim.
"It could be items such as wigs, hats, clothes, gloves and footwear. It's apparent this was a planned and prepared-for crime, and that Mei's killer was forensically aware and has taken steps to avoid being caught.
"It's quite possible they left the address in a completely different set of clothes to those they arrived in."
Mr Preston's car was identified as "a vehicle of interest" having been seen in Miramar the day Ms Fan was murdered.
"No assumptions have been made about who was driving the vehicle," Mr van den Heuvel said. "We want to know who was in it, what were they wearing, where were they going.'
The car, a 1992 bronze Toyota Corona sedan, has a missing passenger-side hub cap and a black strip along the side. Police released a picture of the vehicle asking for sightings from the public in December. Mr Preston confirmed the car in the photograph was his.
The night the body was discovered, he was arrested by about 30 police and armed offenders squad members, he said. He was vigorously examined but no evidence linking him to the crime was found, he said.
The past five months had been gruelling emotionally, he said through tears, because he was unable to see his children, aged 9 and 7.
"As distraught as I am about my ex-wife, it's the kids [that matter]. There's nothing I can do anymore about my wife, I wasn't there to protect her. It's a husband's job to look after his family and I failed in that sense. But I'm not going to fail my children.
"I want to visit with my children. Even just a phone call. Even just to stand across the road and wave. All I want is to see my kids.'
Mr Preston said he was scheduled to fly out to China for a month on Wednesday as he tried to get on with his life.
But as long as the murder remained unsolved, he would have it hanging over his head, he said.
"At this rate, it's my unprofessional opinion that they're never going to find the killer now. It's gone past the all-important time. So this is my life until somehow they figure this out."
