A probe by the garda ombudsman into whether failings in a garda investigation may have contributed to a young woman's decision to take her own life has concluded after gardaí finally located a key statement lost nine years ago.

The Roberts family, from Gathabawn, Co Kilkenny, won a civil action in 2007 against their neighbour, whose sexual assault on their daughter led to her suicide.

Jane Roberts (26) took her own life in 2000, 18 years after being assaulted and sexually abused in a public swimming pool in Thurles, Co Tipperary.

David Roberts from Gathabawn, Co Kilkenny, sued his neighbour John Bowden for his daughter's wrongful death in 2007 and was awarded €25,395 at Clonmel Circuit Court. It was a landmark case and the first of its kind.

The young woman made a complaint to gardaí against Bowden in 1999. She was frustrated when there was no news on whether Bowden was to be prosecuted after she made a statement, her father said. Shortly afterwards, she killed herself and criminal proceedings could not be initiated.

It later emerged the DPP requested more information from gardaí before it could give the go-ahead to lay charges.

For an unknown reason, investigating gardaí did not provide the DPP with the additional information it requested for five months. The DPP finally received the additional information three weeks after Roberts had died.

Dave Roberts complained to the garda ombudsman about this failure of gardaí to provide information to the DPP. But following a lengthy probe, the ombudsman concluded it could not investigate this matter as it would "impinge on the rights" of the DPP's office.

"Possibly through human error, gardaí didn't provide the DPP with the information requested for five months. Then a few weeks after she died, it suddenly landed on his desk. Where was it lying for five months and did this influence the DPP's decision not to prosecute? We just don't know whether if gardaí had acted quicker, Jane might not have taken her own life. That's something we will never know.

"The ombudsman said it could not investigate the garda delay as it involved the DPP," said Dave Roberts. "We could take a judicial review of this decision but it would be at an extensive cost. It has been a long road. I think it has gone as far as it can."

It is understood John Bowden, who admitted the sexual abuse during the civil case, is suffering from prostate cancer and has a limited life expectancy.