Michael James Holt, 26, planned a mass shooting at Westfield Tuggerah before a Crime Stoppers tip-off helped foil his deadly plot. Picture: Fairfax

By the time he was in his 20s, he was stockpiling homemade guns and talking about carrying out a mass shooting at a Westfield shopping centre.

Now Michael James Holt, 26, is set to face the music after pleading guilty to multiple firearm manufacture and possession charges stemming from raids on three properties on the NSW Central Coast in 2015.

On Friday, a NSW court heard that Holt, who is autistic, has been “obsessed” with firearms since he was five years old.

Described as an angry “genius” and a fully radicalised white supremacist, Holt’s frightening fantasy was revealed in court papers obtained by Fairfax Media in late January.

Holt, a failed business student, had reportedly talked about carrying out a mass shooting since he was at school.

“Of particular concern, it was reported that the offender often talked about loading weapons into his vehicle and driving to a very public place where he would ‘just start shooting it up’ most recently saying he wanted to do this to Westfields at Tuggerah,” the statement of facts tendered in court revealed.

A tip-off to police led them to Holt in July 2015.

In the Penrith District Court on Friday, Judge Jeffery McLennan said Holt, who suffers from autism spectrum disorder according to Dr Oliver Nelson, had a “lifelong obsession” with “incredibly dangerous weapons”.

Defence barrister Paul Bodisco said Holt’s views and possessions of the guns were “causally related” to his autism disorder, adding he also had a strong interest in Lego which did not manifest in the way his obsession with guns did. “The reduced range of emotional responses and a rigid and rather lateral thinking, in my submission, allowed him to engage in this type of behaviour and in Dr Nelson’s words, beyond the normal range of obsession,” Mr Bodisco said. “These issues became if you like profoundly deleterious to his function as he grew into adulthood.”

He had been making guns, knuckle dusters and slingshots in his grandfather’s northwest Sydney garage.

Until his arrest in September 2015, he lived between his mother’s house in Windsor, his grandfather’s house in nearby Hobartville and a hotel in Ourimbah.

At the Tall Timbers Hotel, police found eight guns, a flick knife and a slingshot.

Many of the homemade guns were described as “slam fire” guns, which are only capable of firing a single shot.

Pipes and other gun parts, hand drawings relating to making guns, Nazi memorabilia and white supremacy propaganda were also found.

Fairfax Media reported Holt has Asperger’s syndrome and low intellectual capability, though his homemade guns showed incredible skill.

On one online profile, he described himself as “anti-system, anti-religion, anti-politics, pro-gun”.

He listed his job as boss of the Reaper’s Disciples Private Security Company and wrote: “I will do anything for those i love” and “Ausfailia can go to Hell”.

Holt is due to be sentenced in Penrith Local Court today.