A senior police officer has been accused of being resistant to investigating the death of showjumper Katie Simpson as a murder.

The 21-year-old died in hospital six days after an incident in a house in County Londonderry, in August 2020.

In the months after Katie’s death police treated her death as suicide before it was upgraded to a murder investigation.

The Police Service of Northern Ireland (PSNI) said Katie Simpson’s murder has left a family devastated and they continue to suffer unimaginably.

At the time of Katie’s death, Det Ch Insp John Caldwell led a major investigation team based at Maydown PSNI Station in Derry.

Alliance MLA Nuala McAllister, a member of the Policing Board, has told a BBC Spotlight investigation that a police officer from another team, who was trying to push for an investigation, was getting pushback.

“I am aware that there was an individual officer who did a lot of work and actually brought it forward to his superior to say: ‘This isn’t right here.’

“He met a lot of resistance, not from his superior but from within the team around the district in which Katie lived and where the death actually occurred,” she said.

“There was a police team in the PSNI who just didn’t want to know. I’ve been informed that it was DCI John Caldwell who led that team.”

Det Ch Insp Caldwell is one of the best-known detectives in the PSNI.

In 2023 he survived a dissident republican gun attack and was awarded the King’s Police Medal.

Ms McAllister said: “It has been alleged to me that it was DCI John Caldwell himself who put up the most resistance and acted in the way, I have been told, that was not befitting of a senior ranking officer.

“Why fight it? Why argue against it? Where was the harm in investigating it?”

In January 2021 a police team in Armagh became the lead investigators of the case over the Maydown team.

Ms McAllister said: “Why did it take a major investigation team in a different district in Northern Ireland to actually start the investigation into Katie’s murder?”

A separate police whistle-blower has told the BBC: “Something had gone very wrong for the major investigation team in Armagh to have to take the lead over Derry. That’s a fact. I don’t know what that was but it stinks.”

In March 2021, Jonathan Creswell was charged with the rape and murder of Katie Simpson.

Creswell was a showjumper turned horse trainer who was in a relationship with one of Katie’s sisters.

His trail began earlier this year, on 23 April.

It heard that he had previous “illicit” sexual relations with Katie and attacked her after discovering that she was in a relationship with someone else.

He had then tried to cover up what had happened in a “calculated and deceitful“ way by claiming her death was as a result of suicide.

Creswell was found dead in his home on the second day of the trial.

In a statement, PSNI Chief Constable Jon Boutcher acknowledged that there were shortcomings in the initial stages of the investigation and said he was sorry for this.

He added that following an investigation by the Police Ombudsman, misconduct proceedings are under way against some officers but confirmed that Det Ch Insp Caldwell is not one of them.

Det Ch Insp Caldwell, the chief constable said, almost gave his life in public service and he and his family have the PSNI’s full support while his recovery continues.

He added said that the challenge of immediately identifying the circumstances of a death where a perpetrator as devious and manipulative as Creswell is involved should not be underestimated.

Jonathan Creswell first met Katie and her family through working in horse stables near their home in Tynan, County Armagh.

He went on to have two children with Katie’s eldest sister, Christina.

It was a controlling relationship.

“He isolated the family,” said Marie Brown, CEO of Foyle Women’s Aid and the Family Justice Centre.

“Coercive control, I believe, is one of the most insidious forms of abuse because it gradually is undermining somebody, instilling fear, paralysing them from telling anybody because they’re so fearful of that person.”

By the time she turned 18, Katie mostly lived with her sister and Creswell, under his control.

On August 4 2020, he claimed to be the good Samaritan who had found Katie injured after she had attempted suicide.

The emergency services were alerted and Creswell put her into a car to bring her to hospital.

BBC Spotlight has obtained extracts of the actual call between Creswell and the 999 call handler.

They include Creswell pretending to undertake CPR while waiting for an ambulance to arrive.

“One, two, three, four,” he counted out.

“I think I’m hurting her. One, two…”

During that time he unlocked Katie’s phone and turned on airplane mode, so it could not be tracked.

In hospital, the 21-year-old was put on life support.

She never regained consciousness.

“Her eyes flickered a bit,” her mother, Noeleen Simpson, recalled.

“Just a lot of frustration coming from her, an awful lot of anger coming from her.

“There were a couple of marks. I remember saying to the nurse: ‘What’s this?

“And the nurse said she didn’t know – but she did look concerned.”

Katie’s bruises were of concern to nurses; she had also presented with vaginal bleeding.

A post-mortem examination noted injuries to her limbs “consistent to being struck with a rod-type implement”.

Creswell had a conviction for a catalogue of physical abuse against another woman within the showjumping world.

Ten years previously, in 2010, he had been sentenced to six months in prison.

The PSNI has been criticised for missing a number of red flags in the 24 hours after the incident alone, but Creswell misled them.

However, many suspected he had harmed Katie.

His arrest in March 2021 came months after several people, including family members, a nurse and others repeatedly contacted the police in order to try and get Creswell treated as a suspect in the death of the young showjumper.

What Katie’s family and friends did not know up to that point was the extent to which Creswell controlled her young life.

“I just can’t believe she smiled so much with all the abuse that she had to take,” said Noeleen.

“I didn’t know what he was like. He was a very cunning man.”

Creswell’s death meant he was not convicted of the rape and murder of Katie.

“I believe that ultimately by him taking his own life, that Jonathan Creswell did get away with murder,” said Ms McAllister.

• Spotlight’s Katie: Coerced and Killed is on BBC One NI Tuesday 23rd July at 21:00 and on BBC iPlayer.

• If you have been affected by any of the issues raised in this article information about help and support is available on the BBC Action Line.