The defence has kicked off their case in the Philip Polkinghorne murder trial.

The Auckland eye surgeon's accused of killing his wife, Pauline Hanna, in their home in 2021.

The defence says Hanna took her own life.

It called its first witness, Pauline's sister Tracey, who believes Hanna took her own life.

The Herald's Craig Kapitan told Heather du Plessis-Allan Polkinghorne's defence lawyer has argued if it's murder he would have had to do it with no mistakes.

He says the lawyer's argued there's no forensic evidence to back up the crown's case.

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