He was speaking after Labour MP and former criminal lawyer Russell Fairbrother called for a review of the right to silence for criminal suspects.
The call followed the acquittal on Thursday of Chris Kahui of the murder of twin sons Chris and Cru and the police announcement that no-one else would face charges related to the killing.
The police investigation was hampered early on by the refusal of the twins' family to co-operate.
Sir Geoffrey, a Law Commissioner, said a discussion about a possible law change was a good one to have, but any change would take time.
"It is not a change that would happen quickly, but talking about it is not wrong," he told the New Zealand Herald.
However, he added that the right to silence was deeply embedded in New Zealand law and there was no question that there were arguments on both sides.
Mr Fairbrother, MP for Napier, said he didn't know if Mr Kahui was "truly innocent" or had received the benefit of the doubt.
"But I do know that someone in that house truly knows what happened," he said.
"It cannot be right that a guilty person is avoiding criminal sanction for this most heinous of crimes."
Mr Fairbrother said New Zealand today was different from old English society, which developed the law to protect powerless suspects against the overwhelming power of the state.
However, Law Society criminal law committee convenor Jonathan Krebs said changing the "cornerstone" law was an unnecessary reaction to what had been a very difficult case.
Auckland University associate professor of law Scott Optican said calling for a review was ridiculous.
Although police could not force people to speak before a trial, they could call them as witnesses in court, where they had to speak.
Meanwhile, the twins' mother, Macsyna King, did not hate Mr Kahui or believe he was guilty, her younger sister, Emily Hepi, said.
She also said Ms King, whom the defence suggested during the trial might have been responsible for the boys' deaths, wasn't the killer.
But she refused refused to tell the Herald who the family thought the killer was, saying "only that person knows".
Ms Hepi said Ms King and the family "just want to move on with our lives, without this kicking us in the arse any more".
She said she had supported Ms King financially over the past two year by employing her in her painting business.
This was because Work and Income had cut Ms King's benefit and no employer "will touch her with a 10 foot barge pole".
