A SENIOR Catholic Church leader has admitted to a court that he does not believe the altar boys who are central to his sex abuse cover-up trial were abused by a paedophile colleague.

The Archbishop of Adelaide Philip Edward Wilson, 67, continued giving evidence in his own defence on Thursday after a fourth, last-ditch, bid failed to have the landmark prosecution dropped earlier in the week.

The Archbishop, then a local junior priest, has become the world's highest ranking church official to stand trial accused of concealing historic abuse of young boys in the 1970s and 1980s.

Prosecutors allege the Archbishop, who has early stages of Alzheimer's disease, was repeatedly told about a paedophile colleague's horrific crimes but failed to inform police between 2004 and 2006.

He has testified that he had "no memory", of two alleged conversations in 1976 when he was told a paedophile colleague had sexually abused local boys.

But under cross examination on Thursday, he told Newcastle Local Court that he "did not believe" that three boys were abused by Father James "Jim" Patrick Fletcher.

After consistently denying he had been told of the harrowing abuse that his former flatmate had inflicted on Peter Aiden Creigh, then 10, he admitted he thought the claims were false.

This was despite the former altar boy, now 57, giving "trustworthy testimony" that detailed how the Archbishop had a "look of horror" when told one night after a Hunter Valley youth group how Fletcher had "punished" him through sex acts.

Fletcher, 65, died in prison in 2006 while serving a 10-year prison term for abusing another altar boy.

As Mr Creigh watched from the public gallery, prosecutor Gareth Harrison asked the Archbishop: "Do you believe now that Mr Creigh was sexually abused by Fletcher, do you believe that now?"

The Archbishop replied: "No. I would have to have that confirmed by either an admission by Fletcher or a process of law."

After Mr Harrison pointed out Fletcher had died, he again asked if he "believed" Mr Creigh's claims.

"In the technical way you are talking about … that is true."

But he began to explain that in "everyday" language he might, as Mr Creigh had given "trustworthy testimony".

Prosecutors claim that same year he was told in confession Fletcher had abused another victim, but accused the altar boy of lying because Fletcher was a "good bloke" and ordered him recite 10 "Hail Mary" prayers.

He had earlier told the court he also refuses to believe two other unnamed altar boys, including the male who made the confession statement, were abused by Fletcher.

He also refused to comment on the confession statement due to church law.

The Archbishop denied wanting to cover up sex abuse to "protect the reputation of the church". He has now finished giving evidence.

Outside court, victims and their families were visibly emotional.

The trial continues.