Police failed to adequately protect a woman who was later killed by her ex-partner, an investigation has found.
Laura Stuart, 33, was subjected to two years of “distress, isolation and humiliation” before being killed by Jason Cooper as she left a Denbigh pub.
An Independent Office for Police Conduct (IOPC) investigation probed the 18 contacts made with North Wales Police before her murder in 2017.
The force said it had now changed how it deals with domestic abuse calls.
One officer has also been found guilty of misconduct.
“Reports made to police included allegations that Mr Cooper had used violence, made threats, had financial influence over Laura, attempted to remove her from the house following arguments and had threatened to distribute intimate photographs of her,” said Mel Palmer, of the IOPC.
“These behaviours were likely to cause Laura distress, isolation and humiliation and escalated over the two years leading up to the tragic events of 12 August 2017.”
Welsh Women’s Aid said the case was a “stark reminder” of the “devastating impact” of domestic abuse and called for more effective training for officers.
The attack happened as Ms Stuart walked home from a night out and she suffered stab wounds to her back, head and chest, internal bleeding, and a fractured nose and cheek bone.
A friend who tried to help was also stabbed.
After Cooper was found guilty of murder and sentenced to 31 years in prison, Ms Stuart’s family said she had been “let down”.
Her mother Liz Griffiths said: “They could have done more for her.”
During the trial, jurors heard Ms Stuart was told to “run” because Cooper was “going to kill her” and “erase” her.
She was also falsely accused of having a relationship with another man, and Cooper threatened to post naked photographs of her online.
Between August 2015 and August 2017, 18 reports were made to police, including allegations of assault and verbal altercations.
The IOPC investigation looked at why Cooper was not arrested or his phone seized to investigate allegations of harassment, stalking or malicious communications.
However, it did find police made “numerous, unsuccessful attempts” to get accounts from Ms Stuart of two allegations of assault.
But officers did not pursue safeguarding measures despite referring her to other agencies.
Following the report’s publication, Ms Palmer said the “range of characteristics and dynamics” of domestic abuse mean police officers need to be “vigilant”.
“Incidents that may be perceived as low risk need to be viewed as part of a bigger picture so that forces view risk holistically to better safeguard women like Laura,” she said.
Since the murder the force has made changes, including making it best practice for officers to activate body-worn video equipment when attending domestic abuse incidents.
It has also employed a trainer and staff will be educated in dealing with different situations.
Supt Nick Evans said the force accepted the findings of the IOPC.
“This has led to improvements in our policy and how we deal with domestic abuse incidents, more training for front line officers and investment in more domestic abuse specialists,” he said.
A spokeswoman for Welsh Women’s Aid said: “It is vital police forces across Wales have effective training to identify and effectively investigate all incidents of domestic abuse, including coercive controlling behaviour and stalking and harassment which is at the centre of many survivors’ experiences of abuse.”