An inquiry examining the convictions of Kathleen Folbigg for killing her four children has released letters the mother wrote from jail about the "black moods" referred to in her diaries.
A second judicial inquiry is looking at the convictions of Folbigg, 55, for the deaths of Sarah, Laura, Caleb and Patrick, who were all under the age of two.
They died on separate occasions in NSW's Hunter region, between 1989 and 1999.
At her 2003 trial, the Crown maintained Folbigg smothered her children, but she said they died of natural causes.
The discovery of a rare gene mutation in her two daughters that causes sudden death, has cast doubt on her convictions by some experts, but the mutation has not been found in her two sons.
More than 100 pages of letters have been tendered to the inquiry this week, which Folbigg wrote in jail to her friend, Tracy Chapman.
In the letters, dated over a number of years, Folbigg wrote that she "got a huge raw deal" before the courts and struggled to cope in jail, laying awake at night because of the noise.
"I've been trying to keep depression at bay. Not an easy fight in here," she wrote in March 2003.
"(The noise is) so bad at times. I have unsavoury thoughts about the noise makers (which is) so not like me, ha.
"Stuffin [sic] tissues in my ears ... just to muffle it enough so I can sleep at all. Certainly a test in sanity and control that's for sure. Give me screaming kids any day after this experience."
In a letter dated February 2005, Folbigg wrote: "While my name is attached to words like 'serial killer', I have no hope of ever being heard fairly or otherwise."
In May the same year, she wrote that her previous diary entries "sounded atrocious" because she was not in a positive frame of mind.
Folbigg explained the "black moods" she referred to in her diaries was her depressive state.
"Not black as in evil, or nasty or murderous. Just dark as in the colour black," Folbigg wrote.
"The (diaries) were used to 'dump' every negative emotion, feeling, thought, I ever had."
The Crown had argued before Folbigg was convicted that her diaries, which included entries about her struggle with motherhood, were admissions of guilt.
But experts who have since analysed the material, will give evidence that they were a coping mechanism for a grieving mother.
Genetic experts have told the inquiry it was likely the rare gene mutation, CALM2G114R, contributed to the deaths of her two daughters.
Folbigg has five years left to serve of her 25-year sentence.
The inquiry continues before retired Chief Justice Tom Bathurst.
