Hoddle Street mass killer Julian Knight has always claimed he went on his murderous rampage as a result of being bullied at the Duntroon Military College where he served as a cadet in 1987.
But cartoons drawn by Knight when he was a year-12 student at Melbourne High School show he was having dangerous fantasies of military-style mass killings two years earlier.
In his four-panel cartoon, Knight's hero - a frail mouse called Seymour - is shot but makes a remarkable recovery to exact revenge, killing 16 enemies in one frame.
In the final image, he draws his hero "Rambo style" carrying a machine gun surrounded by bloodied corpses.
The drawings, which have remained hidden for 32 years, have been examined by an expert clinical psychologist at the request of the The Age.
The psychologist, who wishes to remain anonymous, said: "It looks very much like a rehearsal."
"Of note here is the somewhat chilling level of detail and operational foresight. Reminiscent of the actual methodical manner Knight went about his deadly Hoddle Street killing spree."
On August 9, 1987, Knight, then 19, fired 200 rounds of high-grade ammunition, killing seven people, wounding a further 19 and hitting the police helicopter out of the sky before he surrendered.
The incident happened about two weeks after he was discharged from the army, where he had enlisted as an officer cadet.
He has previously claimed he was carrying out a spontaneous military fantasy in which he thought he was in a battle. He also claimed it was bullying at Duntroon that sent him over the edge.
But the forensic psychologist said the cartoons suggested "fantasy as rehearsal for later stage real-life action".
A fellow Duntroon student has said of Knight: "He was a wimp. A big man when he had a big gun in his hand. He was.a 'Rambo' soldier, you know, the type you see on the screen - one man against the world sort of thing." (Exactly reflected in his earlier drawings).
A Melbourne High School classmate said Knight was obsessed with weaponry and was "bright, cheeky and funny but a bit of a weirdo". "He was a teenaged smart-arse like we all wanted to be," he said. "None of us anticipated he was capable of something like that (the mass shooting)."
Knight was sentenced to life in prison with a minimum of 27 years. In 2014, the then coalition government brought in a one-off law to ban him from ever being granted parole. His appeal to the High Court was rejected earlier this year.