The acquittal of Murray Foreman for the murder of Hawke's Bay farmer Jack Nicholas has forced the spotlight on the issue of paying witnesses to testify -- a practice that is now likely to stop.

The defence in the Foreman trial used the proposed payout to undermine the Crown's star witness, Donna Kingi.

The Sensible Sentencing Trust was set to pay $50,000 to Ms Kingi if Murray Foreman was convicted of Mr Nicholas' murder, but Mr Foreman's lawyer, Bruce Squire, QC, said Ms Kingi was motivated only by money and discredited her evidence.

Mr Foreman was acquitted on Wednesday, and trust spokesman Garth McVicar told the Dominion Post it was unlikely rewards for information leading to conviction would be offered in future.

Not guilty verdicts in three murder cases in the past fortnight have stirred heated debate on the justice system, the role of crown prosecutors, and faith in the police.

The other acquittals were those of Chris Kahui, who was accused of killing his twin baby sons in Auckland, and George Gwaze, accused of sexual violation and murder of his 10-year-old niece in Christchurch.

Auckland University associate law professor Scott Optican said any attempt to draw a pattern from the three acquittals was "nonsense".

"You're supposed to have acquittals if there's no evidence. It doesn't mean things have gone wrong with the system. They've gone right."

Solicitor-general David Collins said two other recent, high-profile cases, those of Lipine Sila and Ian Crutchley, had resulted in convictions.

Police and the crown are to review their roles in all five cases.

The other acquittals were those of Chris Kahui, who was accused of killing his twin baby sons in Auckland, and George Gwaze, accused of sexual violation and murder of his 10-year-old niece in Christchurch.

Auckland University associate law professor Scott Optican said any attempt to draw a pattern from the three acquittals was "nonsense".

"You're supposed to have acquittals if there's no evidence. It doesn't mean things have gone wrong with the system. They've gone right."

Solicitor-general David Collins said two other recent, high-profile cases, those of Lipine Sila and Ian Crutchley, had resulted in convictions.

Police and the crown are to review their roles in all five cases.