"Missing" canoeist John Darwin arrived in Panama in July, a neighbour who says she met him has told the BBC.
Patricia Centella de Lopez said he told her that he and his wife Anne planned to live in her apartment block for a year while they looked for a farm.
Mr Darwin is being held on suspicion of fraud following his reappearance after apparently dying at sea in 2002.
Press agency reports say Anne Darwin flew out of Panama on Wednesday night, but her destination is not yet known.
Mr Darwin was arrested by Cleveland Police on suspicion of fraud after walking into a London police station at the weekend.
On Thursday night, police were granted a 12-hour extension to question Mr Darwin, who is being held at Kirkleatham Police Station in Teesside.
Mrs de Lopez told the BBC she had "no doubt" the man who lived in her building was John Darwin.
"Last July I met a new neighbour in the building. When I speak with him, he told me he was new in the building. He told me his name was John," she said.
Mrs de Lopez said he told her he was from Europe and his wife was there doing some business and would join him later.
The last time she said she saw them together was the final weekend of November.
She said they lived on the fourth floor of the building in Panama City while she lived on the second.
Mrs Darwin, 55, has admitted to newspapers that a photo of her and her husband taken last year in Panama is genuine.
She sold the family home on Teesside and moved to Panama six weeks ago.
In a statement released through Cleveland Police, the couple's sons asked how their mother could have let them believe their father was dead for five years.
They said they had been through a "rollercoaster of emotion" since their father's reappearance.
'Rollercoaster of emotion'
They said: "Having seen the recent media speculation surrounding our parents ever since our dad was arrested, we are very much in an angry and confused state of mind.
"In the short space of time following our dad's appearance in London on Saturday, we have gone through a rollercoaster of emotion.
"From the height of elation at finding him to be alive to the depths of despair at the recent stories of fraud and these latest pictures. And the shock of being thrust into the media spotlight.
"If the papers' allegations of a confession from our mam are true then we very much feel that we have been the victims in a large scam.
"How could our mam continue to let us believe our dad had died when he was very much alive?"
Mr and Mrs Darwin's sons said that they had not spoken to either of their parents since their father's arrest.
It has also emerged that both sons have recently left their jobs - one in property and one in insurance.
Cleveland Police said detectives had been given the go-ahead to interview Mr Darwin.
A police spokeswoman said: "John Darwin has been medically examined and has been declared fit for interview."
The spokeswoman said that officers had until just before midnight on Thursday to question him, after which time a superintendent's extension could be granted for a further 12 hours.
Mr Darwin, 57, was arrested on suspicion of fraud at his son Anthony's home early on Wednesday morning. He is currently at Kirkleatham Police Station.