While Philip Sullivan was jailed for rape and sexual assault in the 1990s, he was not placed on the sex offenders' register on his release because his crimes were committed before the register's establishment in 2001.
There is no provision for those convicted of sex crimes before that date to be placed on the register.
Because of this there was no legal obligation on Sullivan to register with the authorities and inform them of his place of residence.
Now that he has been jailed for life, arising from his latest rape conviction, he will stay on the sex offenders' register for life.
Any offender jailed for two years or more for a sex crime can be placed on the register for life on the order of the trial judge.
This will mean that on his release from prison he will be committing an offence if he fails to keep gardaí informed of his whereabouts. He will be required to inform them of any change of address and of any plans he has to leave the State, even for short periods.
Critics argue that gardaí effectively have no proactive role in monitoring registered offenders living in their communities.
The sex offenders' register was established with the enactment of the Sex Offenders Act, 2001.
If imprisoned for between six months and two years, an offender's period on the register is 10 years. For a sentence of less than six months, a seven-year register period applies. If an offender is not jailed, the period on the register is five years.