"I can say categorically that what has been put in various forms in allegations, simply did not happen," an emotional Mr Porter said.

"Nothing in the allegations that have been printed ever happened."

The Attorney-General said he would take "a short period of leave" to assess and improve his mental health.

But he said he would not step down, saying he feared it would set a precedent for other people who faced similar allegations.

"If that happens, anyone in public life is able to be removed simply by the printing of an allegation, every child we raise can have their lives destroyed by online reporting alone," Mr Porter said.

"My guess is that if I were to resign, and that were to set a new standard, there would be no need for an Attorney-General because there would be no rule of law left to protect in this country.

"I am not standing down or aside."

Prime Minister Scott Morrison had said his office contacted the Australian Federal Police (AFP) after it received the anonymous letter last Wednesday.

Mr Porter said he spoke with Mr Morrison on that day and retained the Prime Minister's "full backing".

Earlier this week the AFP said it was unable to investigate the allegation because it was a state matter for New South Wales.

South Australian Police have prepared a report into the death of the woman and the state's coroner will decide whether to launch an inquest.

Mr Porter said he remembered the woman as a "bright, happy person" and they met when she was 16 and he was 17 at a debating event in Sydney in 1988.