Forensic scientist tells murder trial he discounted DNA evidence on jacket belonging to the accused
A forensic scientist in the trial of Mark Nash for the murder of two women in 1997 told the court that he has discounted the fact that DNA profiles from the women were found on the sleeve of a jacket belonging to the murder accused.
Mr Nash, 42, who has last addresses at Prussia Street and Clonliffe Road in Dublin, pleaded not guilty at the Central Criminal Court to the murder of 60-year-old Sylvia Shields and Mary Callanan, 61, between 6 and 7 March 1997.
The two women were living in sheltered accommodation in a house attached to St Brendan's Psychiatric Hospital in Grangegorman at the time of their murders.
Dr Philip Avenell told the court he had compared two hypotheses, one considering whether the DNA results were obtained when the jacket was present at the murders and another whether the DNA results were obtained when the jacket was seized.
He said that reading from his report he was "unable to determine which proposition was more likely."
The court previously heard that a profile taken from the button threads of the right sleeve of the black velvet jacket matched Ms Shields' DNA profile and a DNA profile obtained from a "particle" found inside the seam of the right sleeve of the black velvet jacket, also matched Ms Callanan.
Counsel for the State Brendan Grehan put it to Dr Avenell was he aware of the fact that Mr Nash had said he was wearing the "jacket on the night of the murders?"
"I was aware that scientists had reviewed photos and I saw a photo during the course of the trial" replied Dr Avenell.
Mr Grehan said there was evidence from others like former partner Lucy Porter who said the accused was wearing a "velvet jacket" on the night in question.
Putting forward his reasons for believing how the jacket belonging to Mr Nash was contaminated after it was seized, Dr Avenell said the packaging of the jacket must be considered.
"In this case the top of the bag was rolled over a number of times and sealed with staples, a routine considered at the time to be appropriate, however there is an issue with rolling as it creates crevices where contamination can occur," said Dr Avenell.
Dr Avenell told the court that because wiping down the bag containing the jacket was not a standard practice in 1997, this was another possibility of contamination as blood flakes or particles could transfer to the item.
Dr Avenell told the court that another possible reason for contamination was the fact that the jacket and heavily blood stained clothing and bedding found at the scene were examined in the same room at the laboratory six weeks apart.
The court heard that the fourth possibility put forward by Dr Avenell was "file to file transfer".
Mr Grehan asked Dr Avenell about his theory on the possibility of blood flakes and particles from blood stained clothing and bedding examined in the lab, persisting for six weeks on the floor?
"It’s an unknown variable without knowing the cleaning procedures, we would obviously assume some cleaning was done," replied Dr Avenell.
"There are many steps how this contamination event might have occurred and it is not clear which one," he added.
After Dr Avenell’s cross-examination, Mr Justice Carroll Moran told the jury of six men and five women that this was the end of the evidence and he would resume the case on Tuesday 14 April at 11am, with it finishing the week of 20 April.