Confidence in policing has been shaken "to its very foundations" over the handling of Katie Simpson's murder, Stormont's justice committee chairman has said.
A review published on Tuesday found "institutional misogyny" and "systemic failures" within the Police Service of Northern Ireland (PSNI) during its handling of Katie's death.
Katie, a 21-year-old showjumper, died in 2020 and her death was initially treated as suicide.
Jonathan Creswell, a showjumping trainer and the partner of Katie's sister, was later charged with her murder. He took his own life one day after a trial began in 2024.
The PSNI apologised to Katie's family and said it acknowledged the review.
Paul Frew, who is a DUP MLA as well as Stormont's justice committee chairman, said the review made for horrific reading.
"I spent last night reading it. I didn't get much sleep because of the content within it. It is absolutely astounding," he told Good Morning Ulster.
"So many people have been failed here. They believed this monster even though he had been convicted years before to a six-month prison sentence for bodily harm. It's astounding."
The review found police failed to seriously consider abuse or coercive control during its investigation and instead prioritised Creswell's account.
Warning signs were ignored and Katie's lived experience was disregarded.
Frew called for stronger safeguarding, tougher accountability within the PSNI, and full implementation of coercive control laws to prevent failures happening again.
"Six officers were found to have conducted misconduct," he said.
"Two, I think, were allowed to retire. Only one received a written warning. We can't abide by that."
He added that confidence in the PSNI will need to be rebuilt.
PSNI Assistant Chief Constable Davy Beck said the failings by the force were clear and it did not meet the standards expected of it.
The review found Katie was "let down at every step", criticising police, social services, health services and safeguarding failures within the equestrian sector.
Justice Minister Naomi Long told the BBC that "earlier intervention across the board could have prevented much of the harm Katie suffered".
"There has been a focus, quite rightly, on failures of the PSNI in terms of the investigation of Katie's death and the time following that," she said.
"But there were many and multiple failures by a number of agencies. It would be a failure of this report if the only learning taken from it was from the PSNI."
The report led by Dr Jan Melia said urgent cultural change was needed within the PSNI and warned that misogyny within policing increases risk to women.
It also found 37 other victims - including children - later came forward alleging abuse by Creswell.
"I welcome the fact that the Chief Constable is being proactive about addressing it," Long said.
"Let's be clear, we need to know as women that when we go to the PSNI to report serious crime or when we are in danger, that they take those concerns seriously.
"And that they are conscious of the innate bias that there will be within an organisation that is predominantly male."
Geraldine Hanna, victims of crime commissioner, said she was "profoundly concerned" about what the review found.
"What I find especially troubling though is that since Katie's death we've seen domestic homicide reviews in Northern Ireland continuing to highlight many of the same things," she said.
"So that suggests to me that we're not learning lessons quickly enough or consistently enough."