Collapse of rape case over twins State’s first

THE collapse of a rape case in Limerick because the suspect had an identical twin is thought to be the first such case in Ireland.

The Forensic Science Laboratory (FSL) said it was not aware of any case it had dealt with in which a suspect turned out to have an identical sibling. A number of senior garda sources also said yesterday they were not aware of any other similar case.

The FSL was not in a position yesterday to comment on the specific case in Limerick.

However, the head of the FSL’s DNA section Dr Maureen Smyth said she had not come across a case before involving identical twins.

But she pointed out that they would only be aware of such a situation if they were told by gardaí or the DPP’s office.

In the Limerick case, the DPP issued gardaí with instructions not to proceed with prosecuting a suspect because he had an identical twin. The gardaí had collected DNA evidence linking the suspect to an alleged rape.

Identical twins have exactly the same DNA and, without any corroborative evidence, it is not possible to prove which twin carried out the rape.

“True identical twins have identical DNA profiles because when the sperm fertilises the egg, in an identical twin situation, it’s one sperm and one egg and after fertilisation it splits into two, so it’s an identical genetic dose,” said Dr Smyth. “In non-identical twins, you have two eggs and that’s why they are different.”

Ms Smyth said it was unusual for a case to rest solely on DNA evidence and that there were usually other circumstances, such as fingerprints (which are different among identical twins) and fibres from clothes.

“Generally in our cases there is other evidence. You might have fibres, glass on the clothes, in general some other corroborating evidence, sometimes only slight,” said Ms Smyth.

She accepted that visual identification of the suspect might not be of any use in an identical twin situation.

She said the Limerick case did not mean DNA evidence was of no use in identical twin cases, and that it could prove crucial along with corroborating evidence.

There does not appear to be any central statistics in Ireland on the rate of identical twins. In a report published this week by the ESRI, it is estimated that twins accounted for 1.4% of births, or 873 twin births, in 2003.

Figures from Britain suggest a third of twins are identical. In the book, Twins and Multiple Births, author Dr Carol Cooper said the rate for identical twins was constant worldwide and was estimated to be 0.35% of births.

That would suggest there were 291 identical twin births in 2003 in Ireland.

According to the FSL, the chance of an unrelated person having the same profile as a suspect was less than one in a billion.

The chance of a sibling, including a non-identical twin, having the same profile is between one in 10,000 and one in 30,000.

A spokesman for the Forensic Science Service in Britain said they had “a couple of cases” involving identical twins. “It’s very difficult to know how many and very difficult to say what happened in those cases,” said the spokesman.