In March, former NSW correctional officer Wayne Astill was sentenced to a maximum 23 years in jail for the rape and indecent assault of nine women while working at Dillwynia Correctional Centre in Sydney's west.
The 67-year-old will spend at least 15 years and four months behind bars for abusing his position of authority to commit offences over several years until his suspension in 2019.
A special inquiry is examining the circumstances surrounding the offences and how Astill was able to commit the crimes for so long.
Judy Barry worked as a correctional officer at the Dillwynia centre between 2013 and 2018.
She said no matter how many complaints were raised, Astill was "untouchable".
"People were scared of him, including other officers and inmates," Ms Barry told the inquiry on Monday.
"I used (the term) 'Teflon' myself, because his s*** didn't stick."
Ms Barry said it was widely discussed among officers and inmates that Astill brought prohibited prescription drugs into the prison.
She also once heard inmates signing a song that alluded to sexual acts with Astill in a part of the prison known as "the hub".
Asked if the rumours of sexual activity between Astill and inmates were an open secret among officers, Ms Barry said yes.
"Yes, between officers and inmates (and) that's why there was a song," she said.
A poor workplace culture meant Ms Barry felt like she could not report her suspicions of inappropriate conduct between an officer and an inmate.
Officers were told to use the chain of command within the prison to report incidents and she did not believe she could report it to an external investigation body.
Ms Barry became emotional while trying to explain why she didn't report the rumours and said she felt like she'd let many people down.
"There was no trust, there was no support ... I think there should have been an investigation by our external body," she said.
"At the time I didn't go to anyone (but) now I know I would not hesitate at all to go to anybody who would listen."
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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