Criminologist and author Amanda Howard has gone where few would dare - inside the mind of Australia's most notorious serial killer, Ivan Milat.

Watch Amanda's story in the video above

Milat was arrested in 1994, accused of the murders of seven backpackers, whose remains were found in the Belanglo State Forest.

Following a four-month trial, he was convicted of seven counts of murder and one of ‘detaining for advantage’ in 1996.

Camera Icon The seven known victims of Ivan Milat. Credit: 7NEWS

For more than 20 years, Amanda Howard has been writing letters to and receiving them back from Milat from behind bars.

"He has no problem naming any of his victims," Amanda told Sunrise.

But at the same time, he maintains his innocence.

While the contents of his letters go into graphic detail about what the victims went through, Milat never places himself in the narrative.

"Ivan signs all of his letters just as Ivan ... and underneath he writes 'innocent'," she said.

Camera Icon Ivan Milat photographed in May leaving hospital Credit: 7NEWS

Now with his health failing, Amanda is hoping to get as much information out of Milat before he takes his secrets to the grave.

"He will take his last breath saying he's innocent," she said.

"There's no way there's going to be a deathbed confession."

Originally published as: Inside the mind of Ivan Milat: The woman who has spent 20 years conversing with a killer