Two men who have spent more than a decade in jail for the murder of a taxi firm owner and his girlfriend have appealed against their conviction.
Both men have campaigned to get their convictions overturned
Michael Attwooll, 64, and John Roden, 42, from Risca, Caerphilly county, were jailed for life for the 1994 killing of Gerald Stevens and Christine Rees.
The appeal court in London heard claims that evidence was not put to the jury and Mr Stevens feared being attacked.
The three judges reserved judgement in the case for at least two weeks.
Mr Stevens and Ms Rees were attacked with an unidentified sharp instrument and shot dead at the taxi firm's offices in Risca near Newport on 6 May, 1994.
The prosecution said that Attwooll, who was Mr Stevens's business partner, had enlisted the help of Roden, who was at the time his daughter's boyfriend, to murder Mr Stevens.
Both men have campaigned for their convictions to be quashed and their case was brought to court by a referral from the Criminal Cases Review Commission (CCRC).
Joel Bennathan QC for Attwooll, spoke of evidence, not put before the jury, that he said explained the presence of blood in his client's car and suggested that Mr Stevens was in fear of a potential attack at the time of his death.
He also made strong criticisms of the police investigation.
A statement by one of Attwooll's acquaintances obtained by the CCRC appeared to back his account that he had driven to the office on the day in question, Mr Bennathan said.
"His use of his own car to drive to the taxi offices would have provided significant support for the most obvious innocent explanation for the blood stains later found in that car," he said.
The couple were found murdered at a taxi office in Risca
Mr Bennathan said if the trial jury had seen Attwooll was telling the truth about the journey, it would have boosted his credibility.
Another witnesses had spoken of Mr Stevens fearing he was the intended target of a previous attack on a driver and of him reacting with fear when a blue Ford car passed him.
A similar car was seen near the taxi firm's office on the night of the killings, but the evidence of Mr Stevens' fear was not put before the jury, the QC said.
"The prosecution case against Michael Attwooll always lacked any substantial motive for the two killings," he said.
"The combination of a perceived threat, an earlier attack on another driver and the same type of car being used in the actual area of the shootings very close to the time of the killings could have been enough to raise a doubt as to whether Attwooll, in his white car, had been there at all, " Mr Bennathan said.
Representing Roden, Michael Birnbaum QC said the prosecution case had always been that Roden was enlisted to help in the murders by Attwooll, so for a jury to find him guilty, but Attwooll not guilty, would be "perverse".