A Melbourne IT specialist who allegedly stalked a woman through multiple states remains behind bars as police fear for the safety of his suspected target.

Karl Lawrence Mentzer, 39, allegedly unleashed an 'extreme' stalking campaign against a woman he had been having an affair with before she ended the relationship in January.

The Melbourne Magistrates' Court heard accusations that Mentzer pursued the Sydney woman between January 1 and May 9.

Mentzer - charged with stalking, installing and using an optical device, and using a carriage service to harass - met the woman through their overlapping professions. 

Melbourne Family Violence Unit Senior Constable Jason Randle detailed the allegations of Mentzer's alleged offending to the court.

He said Mentzer and the woman had been in a relationship between July 2024 and January this year which they were 'keeping a secret' because 'they both had partners'.

'He's previously used violence against the victim,' Senior Constable Randle alleged.

Senior Constable Randle detailed an alleged incident in Queenstown, New Zealand, in November last year in which Mentzer caused the woman to fall unconscious. 

The court heard that a friend of the woman had only recently 'warned her' that Mentzer was 'manipulating her' and that she should leave him.

The woman said she remembered nothing except waking up 'confused' in a New Zealand hospital.

Mentzer flew to Sydney in January and allegedly went to a dog park near the woman's house 'where he knew she walked her dog and attempted to see her', the court was told.

In February, the woman had a pre-planned trip to Tasmania, which the court heard 'Mentzer knew about'.

She arrived at the Tasmanian airport to find Mentzer 'waiting in the arrival lounge for her'.

'I will ruin you, I will burn your life down,' Mentzer allegedly said after approaching the woman at the airport.

Mentzer also allegedly sent a drone up to keep the woman 'under surveillance' while she was in Tasmania. 

On March 20, the woman spotted Mentzer allegedly taking photos of her as she entered a building in Melbourne.

On April 3, the court heard that Mentzer travelled to Sydney again where he allegedly took a photo of the woman's husband while he was in a park near their home.

Mentzer then allegedly sent the photo to the woman.

Senior Constable Randle claimed that Mentzer was 'intimidating the victim and showing her that he was near her house' and her 'husband was under surveillance'.

He went on to say that the woman had a pre-booked flight to Melbourne on April 15, which Mentzer was allegedly aware of.

The woman told Mentzer she 'did not want to see him', but it is alleged that he was 'waiting for her' at the airport again.

The woman allegedly had an hour-long phone call with Mentzer on May 3 in which she pleaded with him to leave her alone. 

The woman told Mentzer she 'feared him and his escalating behaviour' and 'did not wish to speak to him again'.

Yet Mentzer allegedly continued to barrage her with messages begging to see her. 

'I feel it is safer if there is space between and distance between us and to break the cycle of hurt,' she responded.

The court heard that Mentzer went on to send the woman messages day and night on May 7.

'I've been in meetings, I'm quite swamped today and I feel quite threatened and scared please stop messaging [and] audio-noting me,' the woman texted Mentzer.

Later in the evening, the woman discovered Mentzer's alleged attempt to be put in the room next to hers when she checked into the QT Melbourne hotel.

The hotel manager said Mentzer had allegedly 'requested' their rooms be side by side.

Staff escorted the woman to a different room on a different floor, the court heard.

Senior Constable Randle alleged that Mentzer installed a spy camera facing into the hotel hallway from his room in an 'attempt to capture footage of the victim'.

The woman wasn't aware of the camera, but police allege they found footage of the hotel hallway on Mentzer's phone.

Mentzer also allegedly barraged the woman with eight phone calls, 31 audio notes and 30 text messages 'throughout the night'.

It is also alleged that investigators discovered photos of a police officer at the Melbourne East police station 'writing notes' and the QT hotel manager on Mentzer's phone.

The woman met a friend at Holy Grail bar on Chapel Street in Windsor for a drink on the evening of May 7.

The two women took a photograph in the photo booth, which the friend later posted to Instagram.

Mentzer allegedly called the woman frequently while she was at the bar and this was 'observed' by the friend.

The court heard that, the following day, the woman spotted Mentzer outside her Melbourne CBD office building just after midday.

The woman attempted to get into her building but Mentzer noticed her. 

She managed to make it into a lift, but Mentzer allegedly put his hand in the doors to stop them from closing.

Mentzer allegedly yelled at the woman accusations that she was 'financially crippling' him and that he was 'meeting lawyers and you won't hear the last of me'.

Senior Constable Randle told the court that the woman was 'cowering in the back of the lift' with her 'hands up, terrified' during Mentzer's alleged tirade.

The woman texted Mentzer soon after he allegedly left her in the lift: 'I am terrified of you.'

The woman then reported Mentzer to police, who said she appeared 'visibly shaken'.

She later shared the Holy Grail image her friend had posted on Instagram but this allegedly caused more problems.

The friend went to Jungle Boy bar in Windsor later that night only to be told by the bartender that a 'male was frantically looking for her'.

The friend said she had no idea who would be looking for her but remembered Mentzer's alleged prior behaviour.

The friend showed a photo of Mentzer to the bartender who confirmed that he was the man looking for her.

The bartender alleged that Mentzer had shown her an Instagram photo of the woman and her friend, and that he had been 'frantically searching for the girls' around different Chapel Street venues.

It is alleged that Mentzer concocted a story saying the 'girls' phones had died' and they were 'really drunk' and he was 'worried about them'.

Victoria Police launched an urgent investigation and Mentzer was arrested on May 9.

Investigators seized Mentzer's phone and allegedly discovered he had hired a private investigator to 'conduct surveillance' on the woman.

Mentzer, who purported to be the woman's 'current partner', sent the private eye the alleged victim's address, vehicle information and her photos.

The court heard the private eye conducted 'static surveillance' at the woman's Sydney home on May 2.

The private eye, who had no idea the woman was not Mentzer's partner, also took video of the woman's husband while at the Sydney address.

Senior Constable Randle said the private investigator had been in contact and had provided key evidence to police.

Police also allegedly found instructions and receipts for spy cameras, secretly recorded vision of the woman and her husband, and search results for the Chapel Street bar. 

Senior Constable Randle said police remanded Mentzer and wanted him kept behind bars for the safety of the alleged victim.

'The contents of the phone show the accused is obsessed with the victim and he's engaging in a pattern of behaviour to locate her,' Senior Constable Randle told the court.

'Police are extremely concerned about his behaviour. As a result of the current incidents, the accused... has been identified in need of immediate intensive risk management due to strong indication he is likely to cause severe harm to the affected person in the coming weeks...

'In the case of the accused, he has displayed the following risk factors which [include]... a recent imminent end of relationship, the sustained stalking and severe controlling behaviours and severe jealousy.

'Whilst there are no definitive means of predicting family violence homicide, the majority of lethal family violence incidents are shown to have previously had one or more of these risk factors [allegedly displayed by Mentzer] identified.

'Meaning, their presence must be taken seriously, a Melbourne Family Violence Investigation Unit plan aims to mitigate these risk factors to prevent severe harm and even homicide in the context of family violence.

'In the view of family violence investigators, the only effective risk-management strategy is to remand the accused in custody.'

Senior Constable Randle also said Mentzer is 'an unacceptable risk of imminently engaging in offending that severely jeopardises the safety and welfare of the victim'.

'The accused has demonstrated that he is obsessed with the victim and is willing to go to any lengths to locate her,' he added.

'The accused has travelled interstate to try and see her and has behaved in an extremely erratic and frantic nature in the current incident, showing her photo to licensed premises to try and get her current location.

'The victim is terrified of the accused and his escalating behaviour which has stemmed from her attempting to end the relationship with him.'

Senior Constable Randle said Mentzer also allegedly 'threatened to share intimate images of the victim' to others, including her husband, which placed her in 'further fear'.

The specialist cop said Mentzer 'appears narcissistic' while 'constantly blaming the victim'.

'The victim is rightfully terrified of the accused and his escalating behaviours, police hold grave concerns for the victim and, as such, has requested the accused be remanded in custody,' Senior Constable Randle said.

Mentzer, who ran a part-heard bail application on Tuesday, will face court on May 25 to learn if he gains release from the Melbourne Assessment Prison.