In a strange and escalating chain of events with no real clues of what might have led there, four members from the family of five emerged from an ill-fated road-trip north cloaked in mystery and mounting concerns from family and police.

"It's out of character," said George Tromp, father of missing man Mark Tromp and grandfather to his shell-shocked children. "He's just a normal bloke like me."

Mr Tromp was last seen running away from the ditched family Peugeot in Wangaratta. A young couple who were out in their own car playing Pokemon Go on Wednesday night, after 10pm, says he "stalked" them.

"I could barely see his headlights because he was that close to my car," said the young man, who asked not to be named. Whenever he pulled over, the Peugeot stopped right behind them. Then the man they insist was Mr Tromp got out and ran towards them, but stopped in the middle of the road and stared. They watched him walk into Wangaratta's Merriwa Park and disappear into the night.

Police believe he had changed his clothes. He left the keys in the Peugeot's ignition.

His wife Jacoba Tromp, 53, is in hospital in Yass, NSW – near Canberra - after being found wandering in an agitated state on Thursday. She had caught public transport, a train or a bus, from Wangaratta on her own.

Prior to all this, children Ella, 22, Riana, 29 and Mitchell Tromp, 25, separately escaped the road-trip, starting on Tuesday. Riana was found distressed beside a highway near Goulburn and is now in Goulburn District Hospital. Ella drove a car back to the family home in the Yarra Valley from Goulburn - a car she did not hire. The silver Peugeot the family set out in is hers.

Mitchell had got out of the car at Kelso, a suburb of Bathurst. He caught trains to Sydney then back to Melbourne. The children have suggested their parents had become more and more anxious and panicked on their way out of Victoria.

Mitchell said there was a "build-up" of pressure that had caused his parents to become "paranoid", thinking they were being followed. He said the road-trip was supposed to be technology-free. He had brought his mobile phone, but threw it out the car window in Warburton.

"It slowly got worse as the days went by. They were just fearing for their lives, and then [we] decided to flee." Their parents pushed on to Jenolan Caves, then Wangaratta, where they were seen together at a shopping mall. Police believe they separated again after this sighting and may be suffering from mental health issues.

However Sergeant Mark Knight of Monbulk is baffled. He knows the family and say they have no diagnosed mental health problems, or drug issues. No-one in the family has accessed a doctor or psychologist recently, or been issued a prescription, he says. They do not belong to any churches, or sects and do not have debts.

Two of the children live at home and all three work seven days a week in the family's successful businesses – a berry farm and an earthmoving company. Daughter Ella has her own company as well supplying trucks and drivers to Yarra Valley farms.

The family moved to Silvan from nearby Macclesfield 10 years ago. Mr Tromp's brother Ken is a police sergeant in Monbulk and is believed to be helping in the search for his brother.

"I am asking myself 'what is going on?'," said Sergeant Knight. "It's a mystery. But there's nothing sinister."

Sergeant Knight said when he checked their home after the first reports of Riana being found near Goulburn, the house was open and keys were in car ignitions, but there was no sign of any struggle.

"This is just a massive melt-down, I'm sure of it. Something triggered them."

Timeline

Monday, August 29: The Tromps leave the family home in Ella's Peugot to go on a technology-free road trip. During the course of the drive, it's discovered Mitchell has brought his phone with him. He throws it out of the window near Warburton, about 32 kilometres from the family home. The family continues driving towards Bathurst.

Tuesday, August 30: Mitch decides he wants to go home. He leaves the family at Kelso, a suburb of Bathurst, about 7am and makes his way to Sydney.

The rest of the family continue on to the Jenolan Caves. That afternoon, they decide to split up. Ella and Riana make their way to Goulburn, but go their separate ways. Riana is found along the highway and is taken to the local hospital due to stress-related issues. Ella somehow acquires a car and drives back to the family home. Parents Mark and Jacoba are reported missing, and that afternoon police attend the family home to find credit cards and mobile phones lying around the house, and car keys in ignitions.

Wednesday, August 31: Mitchell arrives at the family home in the morning after catching the overnight train from Sydney. That afternoon, police search the Jenolan Caves area for Mark and Jacoba, but are unable to find them.

Thursday, September 1: Police are notified in the early hours of the morning that the family car has been located in Wangaratta and that a lone man was seen running the vehicle. It is believed this man was Mark. Later in the day, Jacoba presents herself to Yass District Hospital after a local found her wandering around town. Police continue to look for Mark during the evening, and have no reason to believe he has left the Wangaratta area.

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