The High Court has heard that five other sources corroborated allegations about Gerry Adams that were made by an anonymous contributor in the BBC programme at the centre of his defamation case.
The court earlier heard the 2016 programme did not meet the "editorial thresholds of responsible journalism".
The former Sinn Féin leader alleges he was defamed in the programme and a subsequent online article, which he has said falsely claimed that he sanctioned the killing of former senior Sinn Féin official Denis Donaldson.
Mr Donaldson was shot dead in 2006, months after admitting being an informer for the police and MI5 over two decades.
Mr Adams has denied any involvement in the killing.
This morning, the court heard from London-based John O'Loan, who has 45 years working in broadcast journalism and who was asked by Mr Adams’s legal team to carry out a report into the broadcast.
He said that the inclusion of the anonymous source, known as 'Martin’, lacked sufficient editorial veracity.
He said there were no follow-up questions and no challenge which he said would be normal in a fair and balanced report. "Not only normal, but required," he said.
The first lesson a journalism student learns is to "make sure you can prove it," that is, he said, "to verify."
He also said if you can’t find a second source, "normally you don’t publish."
Under questioning from Tom Hogan SC, representing Mr Adams, he said the allegation made was taken at face value and there was no attempt at rebuttal.
Quoting from his report, he told the court that the programme makers seemed to have "rushed in the home stretch," despite starting cautiously.
He said ‘Martin’ remained anonymous and that neither his motivation nor his background were explained. Mr O’Loan said viewers were offered no means to assess his credibility.
At one point in his evidence, he said he wouldn’t have allowed for publication.
Under cross examination by Eoin McCullough SC, for the BBC, Mr O’Loan agreed that the BBC Spotlight programme has a very high reputation.
Mr McCullough also challenged Mr O’Loan on his evidence that there was no corroboration of the allegation at the centre of this case and said there was BBC document which said the broadcaster had received the information from multiple sources
He said the evidence would be that the BBC had five other sources who supported the allegation.
"That’s ample isn’t it?" Mr McCullough asked.
Mr O’Loan said he could only agree with that if they were "independent sources of sufficient stature."
At one point, Mr O’Loan said he wasn’t there to represent Mr Adams.
Mr McCullough also suggested that Mr O’Loan’s description of ‘Martin’ as "some bloke" was used to denigrate the material.
Mr O’Loan agreed with Mr McCullough that protecting sources is a very serious matter and would justify the redaction of documents. He also agreed that the basic premise was to protect sources, and especially so if there was a risk to life.
He was also asked about his comments earlier in the day, "that’s what’s they would say" when told the BBC said they had five other sources other than ‘Martin.’
Eoin McCullough asked him if those remarks were meant to suggest that what the BBC solicitors were saying were "untrue".
Mr O’Loan denied that and said it was what someone in that position would say. He also said it was hardly a verification of the allegation but said he would apologise if it was a "throwaway" line.
He was also pressed by Mr McCullough on his earlier evidence that the BBC guidelines say the broadcaster is required to produce material for viewers so they can asses the credibility of sources.
Mr McCullough told Mr O’Loan, "that’s something you made up" – a suggestion which Mr O’Loan denied.
At one point, Mr McCullough asked what guidelines were not followed, "we need specificity here," he said.
Later, former US congressman Bruce Morrison gave evidence via video-link from the US.
He was asked by Declan Doyle SC, acting for Mr Adams about the events leading up the granting of a US visa to Mr Adams in early 1994.
Mr Morrison said that Mr Adams is a "controversial figure" but that his reputation was one of being a serious man on a serious mission who was committed to the peace process which brought about the Good Friday Agreement.
He said his word could be taken seriously and could be relied on.
Mr Morrison said he doesn’t know the truth around "various allegations" concerning Mr Adams and said "I know the truth of my dealings" with him.
He went on to describe him as "an elder statesman".
Paul Gallaher SC, acting for the BBC, put it to my Mr Morrison that the reason Mr Adams had been tuned down for US visas was because of "what was considered to be his terrorist connections".
At one point, Mr Morrison said it "only takes allegation to deny a visa".
The case resumes on Tuesday.
