The retired detective - who continues to work for the police in an unsworn role - was consulted before his email was sent to Mr Krebs, Assistant Commissioner Malcolm Burgess told the Weekend Herald yesterday.
"Police will not be disclosing the email pending any action taken by Mr Krebs."
Mr Krebs acknowledged "the responsible attitude" taken by senior police in providing him with the email.
"The comments by this latest officer and those made by former Detective Sergeant Dave Henwood reinforce our grave concern that Mr Pora was wrongly convicted."
Pora has filed an application for the Royal Prerogative of Mercy asking the Governor-General to reopen the case.
Now aged 37, Pora has been in jail for 19 years.
Mrs Burdett was brutally attacked in her Papatoetoe home after an evening out 10-pin bowling.
The 39-year-old accounts clerk, who lived alone, was bashed repeatedly on the head, apparently with a softball bat she kept in her bedroom for protection.
The case horrified the public and baffled police, who had no firm leads for almost a year until Pora volunteered information.
Pora was arrested and convicted in 1994 after making inconsistent confessions he later said were false.
But in 1996, DNA testing showed the semen inside Mrs Burdett belonged to Rewa, who was unknown at the time of Pora's trial but was convicted in 1998 of sex attacks on 24 other women.
Rewa was eventually convicted of raping Mrs Burdett but Pora was convicted a second time of her rape and murder.
Mr Henwood, a multi-award-winning criminal profiler who also helped catch South Auckland serial rapist Joseph Thompson, last month said the reason the juries did not convict Rewa of the murder was that they could not reconcile it with Pora having already been convicted.
Mr Henwood said his opinion that Rewa alone committed the crimes against Mrs Burdett was based on his detailed knowledge of Rewa's "criminal signature", central to which was that he was a lone operator.
The retired detective whose email has been sent to Mr Krebs worked on the Burdett case and shares Mr Henwood's concerns.
Before writing to the Police Commissioner, he spoke about it with another senior colleague, who told the Herald the case was "bizarre" and had polarised police.
"He worked on the case and never felt comfortable [about Pora being convicted]," he said. "I told him that if he felt strongly enough, he should write to the commissioner.
"It wasn't as though he knew anything that could exonerate [Pora].
"It was that things didn't seem to stack up. He felt it was a bizarre situation and he's not the only one who has that view."
The officer, who asked not to be named, said everyone close to the case "has their own opinions, and some of them are quite entrenched".
Additional reporting: David Fisher
