The Firkins brothers have always denied killing the couple
Judgement has been reserved in the appeal of two Somerset men jailed for life for killing a Cornish couple in their own home.
Brothers Robert and Lee Firkins, from Weston-Super-Mare, were found guilty in February 2006 for the murder of Graham and Carole Fisher.
The couple had been beaten and shot in their Wadebridge home in 2003.
The brothers are trying to have their conviction overturned by the Court of Appeal. A ruling is due on 17 December.
The four-day hearing hinged on whether a witness who testified against the brothers at their trial lacked "credibility".
Three Appeal Court judges declined a request to call "witness X" to testify about his reasons for writing a letter in December 2006 to a newspaper reporter, which defence lawyers say casts doubt over his testimony at their trial.
The witness, who is on a protection scheme and cannot be identified, had shared a cell with Robert Firkins.
He told the trial at Exeter Crown Court that his cellmate had confessed to killing 60-year-old Graham and 53-year-old Carole on 5 November at their home next to the petrol station they owned.
Carol and Graham Fisher were killed in their home
At the start of the appeal hearing George Carter-Stephenson QC, speaking for Robert Firkins, urged Lord Justice Hughes, Mr Justice Treacy and Sir Peter Cresswell to allow the witness to be recalled.
But after legal argument Lord Justice Hughes refused the request, saying there was "no basis for doing so".
"There has been the fullest investigation into his letter, and there's no reason to suppose that the letter or anything said about it raises doubt about the truthfulness of his evidence," the judge told the court.
Unable to cross-examine the witness about his letter and possible motivation for writing it, Mr Carter-Stephenson argued that the trial judge should have dismissed the case against the brothers because of the unreliable "cellmate confession".
Robert Firkins, 35, and Lee Firkins, 33, say they were seeing relatives and visiting a local pub at the time of the murders.