Marie Rankin's naked body was found lying on her bedroom floor in her Newry home on Christmas Day 2008, after her family became worried about her when she didn't return their calls.
It is alleged that the 81-year-old had been beaten to death with a crucifix and that she was sexually assaulted after her death.
Her neighbour, Karen Walsh (45), a pharmacist and mother of one, has denied killing her.
Walsh, who is the wife of a top Dublin financier, lived in the Berkeley Court Hotel in Dublin during the week and travelled to her house in Newry at weekends
The Belfast Crown Court jury yesterday heard evidence from forensic biologist Sue Woodroffe who said that DNA taken from Mrs Rankin's chin provided a full DNA match for the accused.
In cross examination, Ms Woodroffe said she did not agree that because the samples on the breasts and crucifix were partial matches "the results were meaningless or inconclusive".
She did accept the traces were so small they could have ended up in those places indirectly.
Ms Woodroffe said the DNA from Walsh on Mrs Rankin's chin was as a result of a direct transfer.
She agreed it was possibly due to an embrace or a kiss, as suggested by defence barrister Peter Irvine, but said it might also have been passed in the course of friction or "rubbing".
Belfast Crown Court also heard from a fingerprint specialist who said the defendant's fingerprints were not found on the alleged murder weapon.
John Brown said neither had any fingerprints been found on two phones and on a back door key from the murdered pensioner's home.
Earlier, William Armstrong, a chemist and principal scientific officer with the Forensic Science Service, said there was "strong evidence" that a wound on Mrs Rankin's face was caused by someone pushing the head of a crucifix into her chin, and "rocking the figurine from side to side".
He said pinprick marks on Mrs Rankin's chin were caused by the crown of thorns on Jesus' head.
Mr Armstrong said he "completely disagreed" with a defence contention that an object other than the crucifix could have produced the bruising and abrasions on the victim's chin. He said he did not believe the marks could have been caused by a nebuliser which the victim used to help her breathing.
The jury at Belfast Crown Court has already heard that a post mortem showed Mrs Rankin had been sexually assaulted, had 15 fractured ribs and had suffered a "multiplicity of blows" to the head.
Walsh, who is married to Dublin accountant Richard Durkin, admits to being in the house but claims she went in earlier in the evening to bring Mrs Rankin a Christmas gift.
The trial continues.