Maria Stubbings, of Chelmsford in Essex, was strangled with a dog lead in 2008 by Marc Chivers, who had already killed a previous girlfriend.
Her brother Manuel Fernandez has told ITV Daybreak that the family have been calling for a public inquiry.
He said: "This highlights issues around domestic violence with one police force but it's actually a national problem."
– Zoe Billingham, HM Inspector of Constabulary
Domestic abuse is a very serious crime, as the tragic cases of Maria Stubbings, Christine Chambers, her two-year-old daughter Shania and Jeanette Goodwin demonstrate. And it's absolutely vital the police get the handling of these cases right for victims.
Essex Police should be recognised for taking the positive step of asking for this issue to be reviewed, and the force has taken a number of important steps to address how domestic abuse cases are handled.
However, there is still more work to do to ensure that victims get the best possible service from their force.
This report recognises the substantial steps that have been taken to make sure suspects are arrested at the earliest opportunity, that calls are dealt with quickly and that intelligence is developed to identify those at greatest risk.
But I also recognise that it highlights several areas where we need to streamline our processes, improve communication, and provide a better service to victims.
– Essex Chief Constable Stephen Kavanagh
There has been some really positive work done so far and I have already acknowledged that there is still much work to be done.
We are very conscious that we must get our response right every single time.
We are committed to helping victims of domestic abuse and we would urge anyone suffering at the hands of a violent offender to contact us immediately.
Repeated failures in Essex Police's handling of reports of abuse were highlighted by the Independent Police Complaints Commission (IPCC) following the cases of:
- Maria Stubbings, a 50-year-old mother of two from Chelmsford, was strangled with a dog lead in 2008 by Chivers who also killed a previous girlfriend.
- The IPCC found there was no assessment of the risk Chivers posed to Ms Stubbings and as a result she was not afforded proper protection.
- Christine Chambers, 38, from Braintree, who was shot dead in 2011, along with her daughter Shania, by her ex-partner David Oakes.
- Ms Chambers had been complaining about violence from Oakes for two years before the murders. The IPCC found the force's response was "inadequate".
- Jeanette Goodwin, 47, was stabbed 30 times by Martin Bunch, 44, in 2011, in front of her husband at her home in Southend, Essex.
- The IPCC found she received an "inadequate response" from Essex Police on the day of her murder, adding that the force did not recognise the need for urgent action.
A police force in Essex, which failed four murder victims, has been criticised over their handing of domestic violence cases.
Repeated failures in Essex Police's handling of reports of abuse were highlighted by the Independent Police Complaints Commission (IPCC).
The report follows the 2008 killing of Maria Stubbings by her ex-boyfriend Marc Chivers, the 2011 fatal shootings of Christine Chambers and her two-year-old daughter Shania by David Oakes and the murder of Jeanette Goodwin at the hands of her ex eight weeks later.
In the report, HMIC inspectors said the force took steps to improve the way it handles such cases but said further work is needed to ensure the risks to victims are properly managed.