Police "missed opportunities" to catch a double killer, an inquiry has revealed, after it emerges the same officers worked on the failed investigations.
The new review into how Sussex Police allowed murderer Robert Trigg to escape prosecution for the deaths of two former girlfriends for years has exposed "potential" shortcomings.
The force has already exonerated its own officers three times prior to the fourth independent review by a different constabulary taking place.
Chef Trigg was jailed for life last year for the murder of Susan Nicholson, 52, who was found dead on her sofa in 2011, and the manslaughter in 2006 of Caroline Devlin, 35, whose body was discovered in their bed.
Despite a lengthy history of domestic violence, officers had treated him as a "bereaved lover" rather than the culprit.
It took Ms Nicholson's elderly parents six years and their life savings to campaign for both their deaths to be reinvestigated.
Now, the force has referred itself to the police watchdog following the findings of the independent review by neighbouring Thames Valley Police.
A spokesperson for Sussex Police 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."
At least two of the same police officers were involved in both investigations and were aware of Trigg's connection to the cases.
But the force did not find the similarities between the cases suspicious.
An inquest never took place after it was determined that Ms Devlin died of natural causes and a coroner ruled that bank employee Ms Nicholson died accidentally when Trigg claimed he rolled on top of her unintentionally while they slept on a sofa.
In the four months leading up to Ms Nicholson’s murder, officers had been called to the flat they shared six times.
Just two days before her murder, he had been cautioned by police for punching her in the face.
Despite the violence that included beating another girlfriend “to a pulp” in 2003, Sussex police ruled out foul play.
Ms Nicholson’s family, however, refused to believe her death was an accident and hired a senior pathologist and a lawyer to re-examine the two deaths.
Last night Ms Nicholson's mother Elizabeth Skelton, 81, 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."
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.
The full report is not expected to be made public for some time, until other independent inquiries are concluded.
The IOPC said it is has not yet decided how to proceed or whether it would investigate the findings.