The main reason for imposing indefinite (as opposed to fixed) sentences is to protect the community.
A judge must consider the potential of future harm that could be caused by the offender, the circumstances of the offenses, medical and psychiatric opinion, and any other matters of relevance.
The longest effective minimum term imposed is 30 years, being served by paedophile Mark Pendleton (an indefinite sentence to commence on the expiration of 27 years) for sexual offences committed against girls between 1977 and 1996, possessing child exploitation material in his cell, and being the ringleader of a conspiracy with fellow paedophiles to abuse children in Thailand.
The longest nominal sentence imposed on one or more sentences of indefinite imprisonment is 30 years, currently being served by serial paedophile Geoffrey Robert Dobbs (Queensland), who pleaded guilty to 124 sexual offences and one count of attempting to pervert the course of justice committed against 63 girls aged between one month and 15 years, including five family members and girls under his care as a teacher and youth leader, between 1972 and 2000.
"[6] In New Zealand, indefinite imprisonment is called preventive detention and is handed down to individuals aged 18 or over convicted of a qualifying violent or sexual offences if it is likely that the offender will re-offend even if given the maximum term of imprisonment otherwise allowed.
[9] In Scotland, the Order for Lifelong Restriction was implemented by the Criminal Justice (Scotland) Act 2003, which gives a judge of the High Court of Justiciary the power to impose a sentence for serious violent and sexual offences, that includes the life imprisonment or detention of the offender.
Should an offender be released from prison or detention they will be subject to more intensive supervision, treatment, and monitoring.
The Model Penal Code, developed in the 1950s, focused on offenders' treatment needs rather than on retribution: generous amounts of good conduct time could be awarded by prison officials.
By the mid-1970s, indeterminate sentencing was under attack, as arguments were made that racial and other invidious biases influenced officials, that rehabilitative treatment programs were ineffective, and that broad, standardless discretion denied constitutional due process and permitted undue leniency that undermined the deterrent effects of sanctions.