The family of a woman murdered by her boyfriend five years after he killed another lover said they are "finally being taken seriously" after an independent inquiry found police "missed opportunities" to catch him.
The findings of the review into Sussex Police's investigations of Caroline Devlin and Susan Nicholson's deaths have been referred to the Independent Office for Police Conduct (IOPC) to decide whether "any issues" should be addressed, the force said.
The full report is not expected to be made public for some time, until other independent inquiries are concluded.
Robert Trigg was jailed for life last July after he was found guilty of the 2011 murder of Ms Nicholson, 52, and the manslaughter of 35-year-old Ms Devlin in 2006.
He was in a relationship with both women when he killed them in their homes, which are barely two miles apart in Worthing, West Sussex.
Ms Nicholson's parents, Elizabeth and Peter Skelton, spent six years, and more than £10,000 of their savings, trying to convince the police to reopen the investigation.
They claim they were "ignored" and "failed" by the force and every public body tasked with holding them to account. They have continued to accuse police of a "cover-up".
Speaking to the Press Association from their home in Goring, 81-year-old Mrs Skelton said: "Finally people are starting to listen to us. Finally we feel like we are being taken seriously.
"The more you look back at it all, the more furious you feel about how it was handled. They made fools of us. We keep thinking 'How could the police do such a thing?'
"It's very important for us that the full reports are made public so this can't happen to anyone ever again."
Mr Skelton, 83, said: "This confirms what we knew all along. They can't just say this was a mistake. We have been going on about this for six years. The evidence was pointing to this the whole time.
"Now we want to see the information they have."
Mrs Skelton, who had a minor heart attack during her campaign for justice, added: "We want to read the findings in full and seek legal advice. We won't rest until all our questions are answered.
"Now is the time for the (IOPC) and (Sussex police and crime commissioner) Katy Bourne to step in and hold the police to account where they failed to do so before. We have been very unimpressed so far."
The news comes as they say they feel "let down" by staff at a council-funded alcohol rehabilitation clinic where Trigg and Ms Nicholson met. This is understood to be one of the subjects of a domestic homicide review due to conclude later this year.
Mr Skelton said: "They would have known of his background and seen they were spending time together. They could have done more to protect her and other women in their care from this dangerous man."
At least two of the same police officers were involved in both investigations and were aware of Trigg's connection to the cases. He had a history of violence towards them and other women he met before and after.
But the force did not find the similarities between the cases suspicious and treated Trigg like a bereaved lover rather than a suspect.
An inquest never took place after it was determined that Ms Devlin died of natural causes.
A coroner ruled that former Coutts bank employee Ms Nicholson died accidentally when Trigg claimed he rolled on top of her unintentionally while they slept on a sofa.
Paperwork seen by the Press Association showed the force investigated its own officers three times but found nothing wrong with their handling of Ms Nicholson's case.
But the double killer's true "Jekyll and Hyde", possessive and controlling character was exposed at his trial when Lewes Crown Court heard he did not call the emergency services after the women died. Instead, he went to the shops to buy milk and cigarettes.
After his conviction, police chiefs apologised, said the families would be offered compensation and that independent inquiries - carried out by neighbouring forces with which it shares resources - would be "without fear or favour".
On Friday, a force spokesman said: "Thames Valley Police have completed an independent review of the investigations. The review refers to potential missed opportunities and we have therefore referred it to the IOPC for their consideration as to the way in which they wish those issues to be progressed.
"We are truly sorry it took so long to get justice, and it is important we learn any lessons and provide answers for the families."
The IOPC said it is has not yet decided how to proceed or whether it would investigate the findings.
Mrs Bourne said she had the "greatest respect" for Mr and Mrs Skelton and had been in "frequent contact" with them, adding: "My thoughts remain with the victims' families and I will continue to offer them my full support."
West Sussex County Council, which funded the alcohol rehabilitation clinic, said it would not be commenting while the domestic homicide review was ongoing.
Surrey Police will now review how complaints about the investigations were handled.