A forensic scientist today told a murder trial jury there are "numerous ways" DNA could have been deposited on a jacket belonging to the accused during a forensic examination.
Mark Nash (42), who has last addresses at Prussia Street and Clonliffe Road in Dublin, has pleaded not guilty at the Central Criminal Court to the murder of Sylvia Shields (60) and Mary Callanan (61) between March 6 and March 7, 1997.
The trial has heard the two women were living in sheltered accommodation in a house attached to St Brendan’s Psychiatric Hospital in Grangegorman at the time.
Defence counsel Mr Hugh Hartnett SC today called the second and last of his witnesses; Dr Philip Avenell, a doctor of philosophy and forensic scientist who has worked on high profile cases on body fluids and DNA profiling.
Dr Avenell told the court he has been involved in several hundred criminal investigations and cold cases within the forensic world including the Stephen Lawrence murder case and the Coastal Path murders.
Mr Hartnett later asked Dr Avenell about his involvement in this case and the examinations he carried out on the material in the laboratory at Forensic Science Ireland.
"Last December I got a phone call from James Macguill solicitors requesting me to become involved in the case. I received documents from Macguill solicitors from witnesses outlining their scientific findings in the case and to have a look at them," said Dr Avenell.
“I understood DNA had been covered from threads on the jacket, there was no reference to physical staining on the jacket, there was no interpretation of how they could have got there from the statements, so I felt the only way was to review the case files,” added Dr Avenell.
On January 9 2015 Dr Avenell told the court he visited FSI in Dublin where he reviewed files and viewed the jacket belonging to the accused.
Later Dr Avenell said he looked at what blood stained items were available and what blood stained items had come into the lab and how had they moved around.
"I tried to understand the continuity of movement and where they came from" said Dr Avenell.
Mr Hartnett put it to Dr Avenell when he "learned a jacket belonging to the accused and heavily blood stained clothing and bedding found at the scene were examined at the same laboratory six weeks apart, you wanted to know what cleaning procedures were carried out on the lab in FSI?"
"There was no formal documentation for cleaning in a lab in 1997/1998, formal documentation came along much later but that was working practice at the time," replied Dr Avenell.
Mr Hartnett said there was a proposition put forward by the State that a six week gap is such, that the risk of contamination becomes low?
"The time period isn't the significant factor, it’s the activities that have taken place and what precise cleaning took place in that period. The cleaning procedures today are very different to those in place then,” said Dr Avenell.
"So DNA can last for some time?" asked Mr Hartnett.
"In certain cases DNA profiles can last for some considerable time," replied Dr Avenell.
Dr Avenell said he requested details regarding the lab cleaning procedures but there were none available.
“From my experience I knew there was potential of blood flakes to be generated but I had no information on how they are removed from that environment” said Dr Avenell.
"Does it give an opportunity for a risk of contamination?" asked Mr Hartnett
“That is a concern and we must consider it in our evaluation and how the DNA could have got onto that item” replied Dr Avenell.
Referring to a picture of a lab in 1994, Mr Hartnett asked Dr Avenell how he would compare this lab with a present day lab which are now constructed to lower the chances of contamination?
Dr Avenell said labs by today standards are designed to minimise the amount of cupboard spaces and minimise the amount of lab equipment so there are no areas where dust can attract or accumulate.
Commenting on the brushing down of heavily blood stained items, Dr Avenell said this releases particles into the atmosphere which will spread around.
"In my experience I have reviewed items that are blood stained and placed it on the desk to look at it, afterwards we would also clean the bench then for examination, then the next day I would find dust present there that wasn't present there before the examination," said Dr Avenell.
Commenting on his DNA conclusions Dr Avenell told Mr Hartnett he would have expected to have seen more blood flakes on the jacket belonging to the accused if it had been present at the killing eighteen years ago.
Mr Hartnett then put it to Dr Avenell that the "limited material" is of significance?
Dr Avenell replied saying: "It is of significance."
"Having seen the ferociousness of the attack, I would find it unusual to find only one blood flake, so finding some blood flakes on the bag would be your expectation,” added Dr Avenell.
Mr Hartnett then put it to Dr Avenell that it’s not the habit of the Dublin lab to examine the bag for debris.
"Its typical in my lab where we have a cold case team, that the first time we examine an item regardless of the issue, we would collect debris from inside the bottom of bag. We would also collect bench debris and none of these exams were carried out when the jacket was being examined," replied Dr Avenell.
The jury previously heard that DNA profiles from the two women killed in Grangegorman nearly 20 years ago were found on a jacket belonging to murder accused Mark Nash in 2009.
Asked to comment on the mechanics of contamination, Dr Avenell said: “I don’t want to speculate on how it occurred, but there are numerous ways DNA could have been deposited on the jacket or on the bag during that examination, there are numerous possibilities and I would not like to speculate."
Commenting on the six week gap and whether it has any significance, Dr Avenell said
“it’s a time frame and you must consider the procedures carried out in that time. After a set period of time, we would carry out a deep clean, absolutely everywhere, there is no clear documents in what happened in the lab."
Mr Hartnett later asked Dr Avenell to summarise his findings in the case.
"In summary in my findings I have considered two propositions, the first was that the DNA had been deposited on the jacket or shortly after the murders, the second that the DNA could have been deposited at some time when it was seized by gardai, I was unable to determine which was more likely," said Dr Avenell.
Counsel for the state, Mr Brendan Grehan SC will continue his cross examination of Dr Avenell on Monday at 11am.
The trial continues.