Life imprisonment in Australia
Life imprisonment in Australia is handed down for serious offences including treason, murder, and commercial drug trafficking by the State and Territory Supreme Courts in Australia.
In New South Wales, the average prison term for murder is 25 years, despite the Crimes Act 1900 (NSW) stating the sentence to be for the remainder of the offender's 'natural life'. Five people have now received natural life sentences for murder in 2009, 2010 and more recently in 2013 when a police officer was shot and subsequently killed, NSW Bureau of Crime Statistics and Research.
With non-parole periods
If a non-parole period is fixed, it must be at least 10 years unless exceptional circumstances exist, or 20 years if the prisoner is convicted of the murder of a police officer or other public official.
The longest overall non-parole period is 45 years and six months, being served by South Australian Michael Barry Fyfe, who stabbed former police officer and fellow inmate Trevor Tilley at Yatala Prison in 1996, where he was serving 17 years and six months for attempted murder, intentionally causing serious injury to fellow inmates and prison staff, escaping lawful custody and dangerous driving causing death.
The longest non-parole period imposed is 37 years, being served by Adam Mikhail and his father Frank for shooting dead convicted drug dealer Frank La Rosa and his wife Kim in an ambush at their Chittering property in June 2008.
The longest non-parole period imposed on a woman is 32 years, being served by South Australian Angelika Gavare, who murdered and dismembered pensioner Vonne McGlynn in November 2008 for financial gain.
Without the possibility of parole
In the most extreme cases, the sentencing judge will refuse to fix a non-parole period, which means that the prisoner will spend the rest of their life in prison. In New South Wales, if the prisoner is convicted of the murder of a police officer, they will automatically be sentenced to life imprisonment without parole.
Notorious criminals serving at least one sentence of life imprisonment without the possibility of parole include backpacker serial killer Ivan Milat (New South Wales), serial sex killer Peter Dupas (Victoria), Snowtown serial killers John Justin Bunting and Robert Joe Wagner (South Australia), sadistic rapist and murderer Barrie Watts (Queensland), Port Arthur gunman Martin Bryant (Tasmania), and serial killer Allan Thompson (Australian Capital Territory).
There are four women serving at least one sentence of life imprisonment without the possibility of parole: cannibalistic husband killer Katherine Knight (New South Wales), black widow Patricia Byers (Queensland), serial killer Catherine Birnie (Western Australia) and one from Queensland, who tortured, raped and attempted to kill a 13-year-old girl, but cannot be named for legal reasons.
Hoddle Street gunman Julian Knight is serving seven consecutive sentences of life imprisonment with a non-parole period of 27 years, as the state of Victoria did not officially have provision for life imprisonment without parole until 1991, and Knight was a young offender, being aged 19 at the time of the murders; due to his age, prosecutors did not make an application to refuse to fix a non-parole period. However, the Victorian Government has drafted new legislation that ensures he will die in jail or will only be released if he is infirm and incapacitated. 
Life imprisonment is mandatory for murder.
A murder conviction carries a standard non-parole period of 20 years, but the sentencing judge can fix a non-parole period of between 10 years and 25 years.
There is also provision for the crime of aggravated murder, which applies in cases of premeditated murder, contract killing, multiple/serial murder, murder of a child under the age of 18, murder with a sexual motivation, and the murder of a police officer or public official.
In the case of an aggravated murder conviction, the sentencing judge can either fix a non-parole period of at least 25 years, or in the most extreme case refuse to fix a non-parole period; the latter option means that the prisoner will spend the rest of their life in prison.
There are three prisoners at present serving at least one sentence of life imprisonment without parole in the Northern Territory: double sex killer Martin Leach, psychopath and necrophiliac Andrew Christopher Albury, and serial rapist and pedophile William Gordon Turner.
The longest non-parole period imposed in the Northern Territory is 30 years, being served by Douglas John Edward Crabbe, who drove his Mack Truck into a motel bar at Uluru, killing five patrons; a parole application in 2013 was rejected. The longest non-parole period imposed for a single murder is 28 years, being served by Bradley John Murdoch, who shot dead British backpacker Peter Falconio.
The only woman sentenced to life imprisonment in the Northern Territory under the current laws is Evelyn Namatjira, who stabbed her younger sister Jennifer after an argument a drinking session and is serving a non-parole period of 15 years.
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