The semen 'evidence'
Traces of semen on the hand of Robert Holohan became a controversial issue and reference was made to it in the victim impact statement by Majella Holohan. However, the evidence was in no way conclusive and would have been hugely prejudicial to a fair trial. By Ruth O'Kelly
The swab taken from the palm of Robert's right hand, detected what has been referred to as semen; certainly sperm heads were seen under a microscope.
However when the authorities tried to determine if these sperm cells belonged to Wayne O'Donoghue, they found the sample was too small for conventional DNA technology which requires some 200 human cells to generate a profile.
Another form of DNA testing, however, was available to the authorities to identify the source of the sperm. The Forensic Science Service (FSS) in England offers Low Copy Number testing – an amplified form of the conventional technology – for these trace amounts of DNA.
The sample taken from Robert's hand was sent to the FSS's Dr Jonathan Whitaker. His first report concluded there was “extremely strong support” for the assertion that the semen originated from Wayne O'Donoghue. The reliability of Low Copy Number, however, is questionable.
Professor Dan Krane, of Wright State University, Dayton, Ohio, who advised the defence team in the trial of OJ Simpson, provided the first public insight into Low Copy Number's shortcomings. He testified for the defence in the trial of Sean Hoey, when he stood trial for the Omagh bombings. Professor Krane's fundamental objection is that Low Copy Number results are, at best, ambiguous.
He argues that, because the sample has been amplified to a greater extent in Low Copy Number testing, so too has background noise – in the same way background noise becomes more audible when a sound system is turned up to full.
Standard DNA result graphs, take the form of a baseline with peaks representing the elements of a subject's make-up which make him or her unique. The Low Copy Number graphs, however, show a baseline which is fuzzy – this is the background noise becoming more dominant to the extent that it can be difficult to distinguish between the baseline and the DNA peaks. That means the scientist looking at the Low Copy Number result has to interpret it way beyond the norm in the field of DNA profiling.
In his first report, Dr Whitaker only considered if the sperm on Robert Holohan's had come from Wayne O'Donoghue or not. He cited odds of 77 million to one that it could have come from anyone unrelated to Wayne O'Donoghue.
However once Wayne O'Donoghue's defence team presented the DNA profiles of another member of the O'Donoghue family, Dr Whitaker's position changed. He considered that the “semen” DNA profile could have three possible explanations: that most originated from Wayne O'Donoghue; that most originated from his relative; or that the sample was a mixture of the two. His final conclusion was that the DNA profile obtained from Robert's handswab was an even mixture. However he was “unable to statistically evaluate this observation”, rendering it meaningless. The authorities here – and Majella Holohan – were left with the knowledge that sperm cells had been found on Robert's hand, but no idea who they belonged to.
Another crucial question, though, was how did those cells get onto Robert's hand in the first place?
Both Dan Krane and a fellow American forensic scientist, Marc Scott Taylor, say the supposition that Robert was a victim of a sexual attack is baseless – and that's because the volume of sperm was so miniscule that it needed Low Copy Number testing.
“The reality is that sperm cells don't travel alone,” says Professor Krane.
“They, they tend to travel in, in astronomical numbers; millions of sperm cells typically are, are moving at once.
“It's much easier to explain a very small number of sperm cells associated with an object by means of a transfer event than it is by means of a sexual assault.”
By “transfer event” he means by touching something else which has sperm cells on it.
Wayne O'Donoghue claimed he had placed Robert Holohan's body on a bathmat as he tried to revive him by splashing water on his face in the O'Donoghue family home immediately after the killing. Tests of that bathmat later detected semen stains containing millions of sperm cells … and conventional DNA tests on those sperm cells were a match with the relative of Wayne O'Donoghue whose profile would muddy the water so dramatically for Dr Whitaker of FSS.
Mr Taylor specialises in DNA transfer. He says sperm cells are spectacularly persistent and transferable. They degrade far more slowly than other human cells and they can even be found in their thousands on clothes washed along with a semen-stained towel. That “semen” arrived on Robert's hand simply by his being on the bathroom mat is highly likely, he says.
“Water on the skin enhances the transfer process,” he says. “You can literally get thousands of sperm cells transferred from the semen stain to the skin. Literally just contact between the skin and that stain on the bathroom mat would transfer the cells. It can happen instantaneously.”
Ruth O'Kelly is a producer with RTE's Primetime. She produced the Primetime investigative programme on the Wayne O'Donoghue case, broadcast on 15 Jan. 2008 the night of his release from prison.