A 22-year-old man from Milton Keynes has been arrested as part of an investigation into the Midsomer Murder-type deaths of two neighbouring pensioners.
Detectives swooped on the house at dawn and are currently searching it.
The man has been arrested on suspicion of committing fraud by false representation and also for conspiracy to defraud.
Two other men, aged 31 and 27, have been arrested as part of the same investigation on suspicion of two counts of murder plus conspirary to defraud and burglary.
The alleged victims are retired schoolteacher Peter Farquhar, 69, and 83-year-old Ann Moore-Martin.
The pair lived in the same street in the affluent village of Maids Moreton, 12 miles away from Milton Keynes.
Mr Farquhar, a prominent churchman and former English teacher at the private Stowe School, died in 2015.
At the time it was believed he had passed away in his sleep.
Ms Moore-Martin lived a few doors away and died in May last year. It was her death which sparked an initial police investigation and was later was handed over to the Thames Valley Police Major Crime Team.
Sources said that the deaths were not initially treated as suspicious but it was later discovered that both pensioners had been the victims of huge "substantial" financial fraud believed to have run into hundreds of thousands of pounds. Both were said to be affluent people.
Detectives were understood to be carrying out toxicology tests on Ms Moore-Martin's remains to try to establish how she died.
A spokesman for Thames Valley Police confirmed today that officers had made three arrests in connection with the murder investigation
He said: "The investigation is in relation to the deaths of two residents of Maids Moreton near Buckingham in Buckinghamshire: Peter Farquhar died on October 26 2015, aged 69 years and Ann Moore-Martin died on May 12 2017, aged 83 years.
"The causes of death are yet to be determined.
"As part of the investigation four properties are currently being searched. These include one property in Milton Keynes, two properties in Towcester, Northamptonshire, and an address near Redruth, Cornwall.
Mr Farquhar was also known to students at Buckingham university, where he was a guest lecturer after his retirement from teaching.
He also wrote novels. His first book, Between Boy and Man, concerns a school chaplain who struggles to reconcile his Christian faith with his gay impulses.