The Royal Commission on Anti-Semitism and Social Cohesion's interim report is expected to offer a glimpse into how two men were able to plan and carry out one of the worst mass shootings in Australian history.
The attack killed 15 people attending a Hanukkah festival at the popular beach in December, prompting the government to eventually launch the formal probe.
Sabina Kleitman's 87-year-old father, Alex Kleytman, was shot in the chest and killed as he shielded his wife Larisa from the gunmen.
Ms Kleitman said the safety of all Australians rested on figuring out what - if anything - went wrong before the attack.
"They will have to do a lot of soul-searching, a lot of thinking and re-thinking of their decision-making and a lot of restructuring," she told AAP.
Asked how the release of the interim report made her feel, Ms Kleitman said: "None of what happened makes me feel good."
"It's not only a matter of how I feel - the effects of this act of terrorism are bigger than affecting the Jewish community only," she said.
"It's about the safety and security of all Australians and whether that report actually shows the way forward to avoid or mitigate disasters of that sort moving forward."
An ASIO review of one of the gunmen cleared him as a potential threat in 2019, according to agency director-general Mike Burgess, who said the men "went dark" to conceal their plot.
"It appears the alleged terrorists demonstrated a high level of security awareness to hide their plot," Mr Burgess told a parliamentary hearing in February.
"In simple terms, they went dark to stay off the radar.
"The grim reality is, as I've said many times, ASIO is not all-seeing and all-knowing. We cannot stop every terrorist, just as we cannot catch every spy."
If ASIO was found to have made mistakes, Mr Burgess said the agency would learn from them.
Sajid Akram was shot dead during the massacre while his son, Naveed Akram, remains before the courts on terrorism and multiple murder charges.
The commission will enter an initial block of public hearings in Sydney from May 4 to 15, addressing Jewish-Australian lived experiences of anti-Semitism.
The interim report will be made public on Thursday morning.