A teenager who planned to set off a homemade bomb in a crowded part of Melbourne's CBD has been given an extra four years' jail after Victoria's appeals court found his jail term manifestly inadequate.
Commonwealth prosecutors had appealed against the seven-year sentence given to the 19-year-old in December for the foiled terror plot, arguing it was too lenient.
On Friday, the Victorian Court of Appeal allowed the appeal and re-sentenced the teen to 11 years with a minimum of eight years and three months.
Chief Justice Marilyn Warren and Justices Mark Weinberg and Stephen Kaye said the offending was particularly serious and the maximum and minimum jail term he received was manifestly inadequate.
"They are well outside the range of sentence that was reasonably open to the sentencing judge in the circumstances of this case," they said.
They said the teen's steps towards rehabilitation were far from complete and despite his youth, general deterrence and denunciation of his crimes were of primary importance in a case like this.
"Unless appropriate weight is given to those considerations in a case such as this, the criminal justice system will not have sufficiently discharged its duty to properly express the community's outrage," they said.
The judges said a strong message needed to be sent to deter other like-minded individuals from indulging in similar conduct.
The teen pleaded guilty to obtaining documents relating to an improvised explosive device (IED) and partially constructing an IED in preparation for a terror act, a crime which carries a maximum penalty of life imprisonment.
Commonwealth prosecutors said his plan was "well advanced" and he had stockpiled five boxes of screws in his bedroom for use as shrapnel.
Other items, including a pressure cooker and encrypted documents about homemade bombs, were seized when police raided his home in May 2015.
The appeal judges said he had shown clear intent to assemble and use one or more improvised explosive devices to cause widespread death and injury.
Prosecutors said if authorities had not intervened when they did, people could have been killed or seriously injured.
They argued the teenager's sentence - which would have seen him released into the community at age 22 - did not reflect the "outrageous, heinous offence", but his defence said he was impressionable and had since renounced his radical beliefs.