The man who's on trial for the murder of Wellington woman Mei Fan sent an email to another man she was seeing, accusing him of arranging a hit.

Michael Preston denies murdering Mei Fan in November 2013.

The High Court in Wellington has been told he sent an email to Tani Hoyhtya in March last year and copied it to Detective Sergeant Andrew Compton, who’s read the email in court.

In it Preston tells Hoyhtya he believed a Chinese hitman had killed Mei Fan.

"I now believe that it could in fact have been a professional hit man for Vietnam or even Indonesia or even one of your local Wellington friends."

Preston said in the email Hoyhyta ways jealous of the fact Mei Fan was seeing other men.

Meanwhile the police officer in charge of investigation told the court details of the weapon killed her were kept confidential.

Michael Preston is charged with murdering his estranged wife in November 2013.

Detective Senior Sergeant John van den Heuvel said while it was known publicly a knife was used, details of where and how it was found, weren’t.

"I'm aware Michael Preston has commented to Graham Bullman that Mei Fan was found with a knife sticking in her. I'm not aware of any breaches of security or mishandling of information by anyone throughout the operation Brussels inquiry."

Under cross examination van den Heuval was asked if it was possible there was a breach in police confidentiality. He said it was unlikely.