The man at the centre of the X case ten years ago was jailed for three-and-a-half years today. He was found guilty of the sexual assault and false imprisonment of a 15-year-old girl.

Imposing the sentence in the Dublin Circuit Criminal Court today, Judge Pat McCartan called him "a serious menace". Sean O'Brien, a separated father of three, with a last address at Swords, County Dublin, had denied the charges.

The 52-year-old had been operating as a taxi driver in 1999 when he picked up a 15-year-old girl in Donnycarney. En route to her destination in the centre of town, he sexually assaulted her twice and detained her against her will in his car.

The teenager memorised his badge number, which led to his arrest. A jury found Mr O'Brien guilty of two counts of sexual assault and one count of false imprisonment on Friday.

Mr O'Brien had received a 14-year sentence in 1994 for unlawful carnal knowledge and sexual assault of a 14-year-old girl. The sentence was reduced to four years on appeal.

Judge McCartan today wondered how O'Brien was ever in a position to operate a taxi. He said that he intended to ensure that this did not happen in the future.

He jailed him for three-and-a-half years and disqualified him from driving for ten years. Mr O'Brien's name will also be entered on the sexual offenders register.

Speaking afterwards, the victim called a three-and-a-half years sentence "disgraceful" for a second offence. She said that she also wants to know how he obtained a taxi licence.

Fine Gael justice spokesman Alan Shatter said that it was of huge concern that a convicted sex offender could get a taxi license. Mr Shatter also said that the sentence Mr O'Brien received was too lenient.

The National Taxi Drivers' Union has called for the strongest possible vetting procedures to be put in place immediately so that the public can be assured all taxi drivers are of the highest possible calibre.