The police investigation into the death of showjumper Katie Simpson was flawed and failed her family, a report by the Police Ombudsman has found.

It identified multiple failures, including a willingness to believe the account of Jonathan Creswell, the man who was later charged with her murder.

The ombudsman also said police were aware from an early stage of the investigation that Creswell had been convicted in 2010 for assaulting another woman.

The report said there had been “a general lack of investigative mindset”, which led to her death in 2020 being treated as suicide for several months.

Disciplinary action has been taken against three officers as a result.

The ombudsman said it had received two new complaints, one of which is linked to the original investigation and includes allegations, which may amount to criminal wrongdoing, against a member of the Police Service of Northern Ireland (PSNI).

It added that the PSNI investigation was hindered by the misleading working assumption that Ms Simpson’s injuries were self-inflicted, despite “multiple reports from members of the public” that Ms Simpson had been the victim of controlling and coercive behaviour by Creswell.

Some police officers had also expressed concern that she had been the victim of coercive control.

In addition to those suspicions, medical staff had also expressed concerns about how Ms Simpson’s injuries happened, the watchdog said.

Officers were also warned at an early stage that she was unlikely to survive her injuries.

However, they failed to give sufficient consideration to gathering physical evidence from her, including taking blood samples and photographs of her injuries.

Ms Simpson, 21, from Tynan in County Armagh, was taken to hospital with serious injuries after an incident in a house in County Londonderry, in August 2020.

Creswell, his sister’s partner, had called 999 and pretended he had found her hanging from a stairwell.

But police later came to the conclusion that he had beaten her before strangling her.

Katie was admitted to Altnagelvin Hospital where she died six days later, having never regained consciousness.

Multiple red flags were missed before Creswell was eventually charged with her murder.

Creswell was found dead at home aged 36 while standing trial for murder in April.

Three women charged with helping him cover up the murder received suspended sentences.

The ombudsman’s investigation found that there were “no effective searches carried out at Katie’s address” after her death and communication devices were not seized.

In addition, no supervisory officer attended the house at the initial stages of the police investigation.

Officers recovered two mobile phones but these were “old devices” used by Ms Simpson and no other action was taken at that time to find her latest phone.

The watchdog’s report said her phone was later found “hidden in a field” after Creswell was arrested in March 2021 and interviewed by police.

The Police Ombudsman chief executive Hugh Hume said: “There appeared to be a general lack of an investigative mindset which contributed to shortcomings in evidence identification and retrieval, scene management and identification, a willingness to accept at face value the accounts from Jonathan Creswell, and ultimately confusion around the ownership of the police investigation.”

Chief Constable Jon Boutcher has accepted there were “a number of shortcomings” in the early stages of the police investigation and has met Ms Simpson’s family to apologise.

He told a meeting of the Northern Ireland Policing Board in August that the PSNI had displayed a mindset which had not been “professionally curious enough”.

Prior to Cresswell’s arrest, several people, including relatives of Ms Simpson, had raised concerns about him.

He had a previous conviction in 2010 for an attack on a woman.

The ombudsman’s investigation, which began in March 2021, resulted in a file of 1,400 pages being sent to the PSNI.

It found misconduct by a number of officers, with their cases dealt with by the PSNI’s professional standards unit.

The investigation followed a number of complaints lodged by Ms Simpson’s family and others, related to the fact that police did not treat her death as murder at an earlier stage.

They are bringing a civil action against the PSNI.

It is understood a number of further complaints related to the case have been made to the ombudsman more recently.

They are now under investigation.