A confidential coroner's report has raised the possibility that a serial killer could be responsible for murdering a number of pensioners.
A report leaked to The Sunday Times said two suspected double murders in Wilmslow, Cheshire, could have been the work of an offender unknown to police.
The first two double killings happened in 1996 and 1999 only two miles apart.
In both cases husbands were previously thought to have murdered their wives before killing themselves.
But modern techniques have led a report to find both cases were likely to have been double murders.
The report, which was written by Stephanie Davies, the senior coroner's officer for Cheshire, called on the National Crime Agency and Interpol to review cases in Britain and Europe to determine if they are related.
It warned: "This individual will not stop killing until someone or something stops him."
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The cases involved the deaths of Howard and Bea Ainsworth and Donald and Auriel Ward, all discovered lying on blood-soaked beds in their nightclothes.
They were judged murder suicides but the report pointed to "a number of inconsistencies which do not corroborate the original manner of death of being murder suicide".
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