Preston told Friend murder of Mei Fan was a 'professional hit job'

Michael Preston in the dock during his trial for the murder of Mei Fan in 2013. Photo / Mark Mitchell

Murder-accused Michael Edwin Preston told a friend his estranged wife Mei Fan was killed in a "professional" hit job.

Detective Graeme Muir told the High Court in Wellington today he examined 60 year-old Preston's social media account after Ms Fan's death in late 2013.

The Crown says Preston killed Ms Fan, 37 in a frenzied knife attack on November 8 that year to gain sole custody of the couple's two children.

Preston denies this.

At the murder trial today, Mr Muir told the Court Preston discussed custody issues and the death of Ms Fan on his Facebook page.

"Bad enough losing a wife but also having my kids taken from me at the same time," he wrote on December 21, 2013.

Mr Muir said Preston added an emoticon of a sad face.

Preston added: "Patience is required. Waiting for bureaucracy."

Mr Muir said a friend then asked Preston if police had any luck finding the killer or killers.

"They've got several ounces of nothing. It's a pro job..." he allegedly replied.

The trial before Justice Joseph Williams and a jury of twelve will take a break later today, resuming on Monday.

It's expected to take several more weeks.

Preston also denies a charge of breaching a protection order.

Detective Sergeant John van den Heuvel said black polypropylene fibres were found over parts of Ms Fan's face and left hand after she was killed.

These "whispy, black, hair-like strands" reached down to her shoulder, Mr van den Heuvel said.

"That was of particular interest to me."

The Crown earlier said these fibres possibly came from a Hallowe'en-style witches hat and wig belonging to one of Preston and Fan's children.

Prosecutors alleged Preston wore the wig on the day he killed Ms Fan.