An investigation revealed that the police were unable to adequately protect a woman who was later killed by her ex-partner.
33-year-old Laura Stuart was subjected to two years of "distress, isolation and humiliation" before being killed by Jason Cooper when she left a pub in Denbigh.
An investigation by the Independent Office for Police Conduct (IOPC) examined the 18 contacts that the police in North Wales made prior to their assassination in 2017.
The troupe said it has changed how it deals with domestic abuse calls.
An official was found guilty of misconduct.
"Reports reported to the police contained allegations that Mr. Cooper had used force, made threats, had a financial impact on Laura, tried to remove her from the house, and threatened to distribute confidential photos of her," Mel Palmer said IOPC.
"These behaviors have probably brought Laura into distress, isolation and humiliation and escalated in the two years that led to the tragic events of 12 August 2017."
Welsh Women's Aid said the case was a "clear reminder" of the "devastating impact" of domestic abuse and called for more effective training of officials.
The attack occurred when, one night after her return, Ms. Stuart suffered stab wounds on her back, head and chest, internal bleeding and a broken nose and cheekbone.
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 was "disappointed."
Her mother Liz Griffiths said, "You could have done more for her."
During the trial, the jury heard that Ms. Stuart was asked to "run" because Cooper wanted to "kill" her and "erase" her.
She was also falsely accused of having a relationship with another man, and Cooper threatened to put naked photos of her online.
Between August 2015 and August 2017, 18 police reports were received, including allegations of assault and verbal altercation.
The IOPC investigation looked into why Cooper was not arrested or his phone was confiscated to investigate allegations of harassment, stalking or malicious communication.
However, it turned out that the police had made "many unsuccessful attempts" to receive reports from Ms. Stuart about two allegations of assault.
However, the officers did not pursue any protective measures, even though they were referred to other authorities.
Following the publication of the report, Ms Palmer said that the "range of characteristics and dynamics" of domestic violence meant that police officers had to be "vigilant".
"Incidents that are perceived as low-risk must be seen as part of a broader context, so that forces can take a holistic view of risk to better protect women like Laura," she said.
Since the murder, the troupe has made changes, including best practice, for officials to enable on-the-go video equipment if they accompany incidents of domestic abuse.
It has also hired a trainer and the staff is trained in dealing with different situations.
Supt Nick Evans said the force accepted the results of the IOPC.
"This has led to improvements in our policies and domestic abuse incidents, more training for front-line officers and investment in more domestic abuse specialists," he said.
A Welsh Women's Aid spokeswoman said, "It is imperative that police across Wales have effective training to identify and effectively investigate all domestic abuse incidents, including forced control, stalking and harassment."