A teen accused of plotting terrorist attacks has allegedly written "concerning" notes about attacks on police, transgender people and "Nazi-type" documents in his prison cell.
The 19-year-old, who cannot be named for legal reasons, is facing explosives offences after allegedly planning multiple terror attacks in Melbourne including a school shooting, university bombing and train derailment.
Victoria Police were tipped off by the US Federal Bureau of Investigation and raided his home in February, allegedly seizing ammunition, handwritten notes and chemicals for explosive devices.
He applied for bail for a second time at Melbourne Magistrates Court on Thursday, where police opposed his release arguing he posed an unacceptable risk to the community.
Counter Terrorism Command Detective Senior Constable Andrew Tucker said police searched the 19-year-old's prison cell on Thursday morning.
He alleged Corrections Victoria staff told police they found notes written by the teen about "attacks against police and transgendered people along with anti-Semitic, Nazi-type documentation".
"There are also reports from (Corrections) regarding his behaviour in custody, which is concerning to police," he told the court.
"One of those has been reported to police, which is a threat against a prison officer, that has been withdrawn by that prison officer since."
He said the teen had written notes in code and plain English, and "physical objects" found in his cell had been reported but did not disclose what those were.
"The way the accused has covered his notes up and possessed violent extremist material ... if he is released on bail he will continue to try and obtain chemicals and continue that behaviour," Det Sen Const Tucker said.
The detective said he was also concerned about a chemical delivery to the teen, which investigators have not yet been able to find, and "secret locations" where he conducted his work that remain unknown.
The teen's lawyer said he was vulnerable in custody due to his autism diagnosis and young age, noting it was his first time behind bars.
His father was called to give evidence about housing the teen in the family home, and said he and his wife plan to supervise their son 24 hours a day if he is released, and if they cannot then an NDIS-approved support worker would monitor him.
The father said his son would not be allowed to use a smartphone and that the parents or support worker would "more intensely" supervise computer internet usage.
The parents previously found chemicals hidden in a cabinet in the teen's bedroom and tried to clean them up, the father told the court.
Sitting behind glass in court, the 19-year-old stared downwards and did not look at his parents as they appeared in court to support him.
Magistrate Malcolm Thomas said while it was clear the teen was from a loving family, he had demonstrated an ability to allegedly offend "under his parent's noses".
He said notes found in the teen's cell showed the "salutary experience" of being behind bars had not changed his alleged radicalisation or ideation.
And further, he feared the man may have access to the chemicals police allege they are yet to find if released.
"The risk that's identified here is ... that the applicant will engage in some form of school shooting or massacre or mass killing," Mr Thomas said.
"The consequence of this eventuating is about as extreme of a risk as you can get."
He will hand down his bail decision on Friday.
