West Midlands Police failed a woman whose former partner stabbed her to death, a watchdog has said.
Rabina Bibi, 35, died after being stabbed at least 15 times in Foleshill, Coventry, in September 2007.
She called police twice on the night of the stabbing and her daughter, aged seven, reported the fatal attack.
The Independent Police Complaints Commission said it would never be known if Ms Bibi would still be alive if police had acted appropriately.
On the night she died Ms Bibi made a 999 call to police from her address in Leicester Causeway as she was concerned her former partner, Zakarya Rezaie, was banging on her front door.
Six minutes later, she rang to say he had left and she did not need police assistance.
Twenty-seven minutes later, at 2009 BST, her daughter made a 999 call to say she was being attacked.
Police attended and found her with severe stab wounds and she died at the scene.
The Independent Police Complaints Commission (IPCC) found that the first call was graded an "early response incident" correctly and meant a police officer should have attended within 30 minutes.
"However, no such police resource was deployed to the first 999 call logged," the report said.
An inquiry did not find out whether the cause was due to IT failure or human error, the report also said.
The second call was treated correctly as the police response was not cancelled and the third call, graded as "immediate response" was also graded correctly.
IPCC Commissioner Len Jackson said West Midlands Police had failed a vulnerable woman, regardless of whether there were IT faults, human errors or performance failings.
"She was entitled to a police response within 30 minutes based on the information she provided and it failed to happen.
"It will never be known whether she would still be alive today, had police officers been despatched to her in accordance with force policy," he said.
The IPCC has recommended a review of supervision in control rooms.
West Midlands Police said it regretted the events of that night and it accepted the IPCC's findings.
A force spokesman said: "Despite the uncertainty of exactly how the delay in responding to Ms Bibi's initial call occurred, West Midlands Police has undertaken a range of reviews to ensure that this cannot be allowed to happen again."
Rezaie, 29, was given a life sentence for murder and told he would serve at least 15 years.
Warwick Crown Court heard he had been unable to accept the relationship was over.