A catalogue of police failures in handling the suspected murder of a young woman in Northern Ireland reflected institutional misogyny, a report has found.

The Police Service of Northern Ireland (PSNI) missed clear warning signs that Katie Simpson’s death in August 2020 was not suicide but the result of abuse and control, an independent review said on Tuesday.

The 21-year-old showjumper had been groomed and subjected to degradation by a violent predator, Jonathan Creswell, but “not one officer thought seriously about abuse/control”, the report said.

Simpson, from Tynan, County Armagh, died in hospital in Derry almost a week after an incident which police originally treated as a suicide attempt.

Seven months later, in March 2021, detectives arrested Creswell on suspicion of murder. The 36-year-old took his own life in April 2024 after the first day of his trial.

The review, led by Dr Jan Melia, said Creswell had masked abusive behaviour behind a charming facade.

“Katie’s lived experience was disregarded, clear warning signs were ignored, established protocols were treated as optional/discretionary, and police chose to privilege Creswell’s account,” she wrote.

Simpson was let down at every step, the report said. “Police inaction rendered her invisible in her own murder, allowing Creswell to maintain control even after death.”

It said 37 people, male and female, had come forward to say they were abused by Creswell, a showjumping trainer who had been dating Simpson’s sister.

Northern Ireland’s justice minister, Naomi Long, who commissioned the report, told the Stormont assembly that police must recognise the existence and gravity of coercive control.

“Katie’s death was concealed and staged as suicide and it is abundantly clear that investigative practices and mindsets must change,” she said, asking assembly members to pause for a moment in memory of Simpson.

The review faulted other agencies, including social services and the health service, but most of its 16 recommendations focused on the police, with an emphasis on training.

In a foreword to the review’s report, Simpson’s mother, Noeleen Mullan, said it had been hard to read and that police had shown her daughter a lack of care.

Kevin Winters, a solicitor representing the family, said they welcomed the report’s highlighting of misogyny.

“The family feel very, very strongly about that and want to put that on the record, and it’s one of the key areas that they’ve been looking to in terms of recommendations.”

Simpson had attended a horse yard close to her home to care for and ride horses from the age of eight. The report found that Creswell, who worked at the yard, groomed her from the age of 10 and inflicted “coercive control, verbal degradation and physical abuse”.

Police initially overlooked evidence of a violent assault and accepted Creswell’s claim that Simpson had taken her own life.

A 2024 report by the Police Ombudsman criticised a “lack of investigative mindset” and said there were no effective searches at Simpson’s address and no supervisory officer attended the house early in the investigation, findings that prompted a PSNI apology.

The independent review identified deficiencies in scene management, neglect of forensic evidence, flawed oversight of suspect history, an inadequate witness strategy, fragmented leadership and limited disciplinary action.

It also cited references to Creswell as a “bad boy” rather than a violent perpetrator and said such language trivialised male aggression and undermined the credibility of female victims.

“This kind of language is normalised, seen as a bit of laugh or banter, but this is part of the problem,” it said. “The use of this kind of language is misogynistic because it protects male perpetrators at the expense of female victims.”

Assistant chief constable Davy Beck said the PSNI accepted the review and would implement its recommendations.

“Patterns of coercive control were not sufficiently understood or challenged, investigative decisions did not always reflect the level of professional curiosity and rigour that should have been applied,” he said.

“The failings are clear, we fell short, and for that I am truly sorry.”

A documentary about the case aired on Sky Documentaries and Now TV in September last year.

• In the UK, Samaritans can be contacted on freephone 116 123 and the domestic abuse helpline is 0808 2000 247. In the US, the suicide prevention lifeline is 988 and the domestic violence hotline is 1-800-799-SAFE (7233). In Australia, the crisis support service Lifeline is on 13 11 14 and the national family violence counselling service is on 1800 737 732. Other international helplines can be found via www.befrienders.org