Timothy Wilson, 65, faced Melbourne's Bail and Remand Court on Sunday afternoon via video link from a police cell on four charges of stalking, along with weapon offences.
The Frankston man, who tried to apply for bail, is accused of stalking four young women between June and September before police arrested him on Saturday.
The women each notified police after they found Apple AirTag devices attached to their vehicles via a magnet and black electrical tap.
One of the AirTags was discovered by mechanics during a car service, the court was told.
When officers searched Wilson's home, they found a plastic bag containing magnets, pieces of black tape and Apple AirTag boxes, a prosecutor told the court.
Investigators also allegedly found a large kitchen knife stuck to a curtain rod and knuckle dusters.
Inside Wilson's garage, police found two "trail-style" cameras, a homemade firearm, multiple audio recording devices and a four-pack of unopened AirTags, the court heard.
Prosecutors allege 30 AirTag devices attached to unknown items and vehicles were found via Wilson's devices.
"Further located throughout his address was a series of diary-style notebooks, containing detailed notes on the listed victims and their vehicles, and further information on their movements," the police prosecutor said.
"These diaries detailed all four vehicles driven by the victims, their day-to-day movements, with clear evidence Wilson was following their movements in his vehicle alongside tracking their movements via the AirTags."
The diaries also contained details of other unknown victims and vehicles "including children's schools and addresses", the senior constable told the court.Â
She said the four alleged victims were living in a state of "constant hypervigilance" and investigators had not been able to identify a motive.
The prosecution opposed Wilson's release on bail due to his risk to community safety and further offending.
His risk was elevated because police found a homemade gun fabricated from steel attached to a "children's soft-style Nerf gun", which appeared capable of firing a 12-gauge shotgun round, the court was told.
Wilson allegedly had a "clear view of corruption" in both Victoria Police and the court system, she said, as she expressed concerns about more potential victims.
"Police believe there to be up to a further 25 unidentified victims with devices installed on their vehicles, and will now begin attempting to identify and notify these persons," the prosecutor told the court.
But Wilson's barrister Nikhil Sood said his client denied the allegations, had never offended before and had compelling reasons to be granted release on bail.
"He has clearly been of some good character when he was younger, because he was part of the police," he told the court.
Mr Sood said it was "not a certainty" that Wilson would receive a prison term if found guilty of the offences.
He agreed the stalking allegations were "extremely concerning" and sophisticated on some level, but he said there was "clearly work to do" on the prosecution's case.
Mr Sood said the homemade firearm was found in pieces and Wilson's defence had not been provided copies of his purported diary entries, only a photo of a stack of books.
Magistrate Samantha Seoud denied Wilson's bail application on the grounds he presented an unacceptable risk of committing a further offence and his release could endanger the safety or welfare of another person.
Wilson was remanded in custody and will face Frankston Magistrates Court on October 9.
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