The 20-year-old, sick of the usual rise-and-grind back home, embarked on a trip-of-a-lifetime, travelling along the east coast of Australia with friends before arriving solo in Warrnambool in March 2005.

It was here he sent packages to his home in Sweden, filled with his personal belongings - books, gifts and photos - along with his return plane ticket and some money his father had lent him.

He then disappeared without a trace.

Warrnambool police Detective Senior Sergeant Chris Asenjo was part of the team assigned to Max's missing person case in 2005.

He said the case was handed to the Warrnambool police crime investigation unit about three months after Max's disappearance.

"As unit commanders, myself, Lee Porter and Andy Raven, regularly reviewed the missing person investigation, as well as triaged and assessed new information that would come in," the detective said.

"Since Max's disappearance, there have been a number of sightings of him from Colac to as far as Byron Bay and Sydney.

"Quite often we get a report of 'I saw this person on a poster at the police station that reminded me of a time I saw someone with that description at this location'."

Detective Senior Sergeant Asenjo said information relating to alleged sightings were sent to local police stations for investigation.

"We would request officers at those stations to take action and unfortunately up until this day, none of the information reported has helped us find Max," he said.

The detective said investigations into missing persons included checks with mobile phone providers and financial institutions.

"We try to put our resources into finding people who still might be out there and might still be contributing to the community in some way," he said.

"Unfortunately, there are also missing people that are on our books that we do believe have clearly passed away. Being on the coast, you do have that possibility of people coming to misadventure on the ocean."

In Max's case, there is no evidence of him being dead or alive.

Detective Senior Sergeant Asenjo said the last contact Max had with his family was when he sent home his personal belongings and a letter.

"He wrote to his family to say he had a bit of an epiphany here in Australia which may have seen him go to a more primitive community,' he said.

"(Max's father) Rolf was of the belief he had joined some sort of community that lives pretty much off the grid and I think he had found some peace with that."

Rolf Castor died without answers in May, aged 77.

Detective Senior Sergeant Asenjo said he had regular communication with Mr Castor, who lived in Sweden, in the 15 years since his son's disappearance.

"In emails to me, Rolf was quite hopeful that Max had met someone, had children and that he (Rolf) may actually be a grandfather," he said.

"We've had no indication that Max is dead and he was a young man in the prime of his life so we do hold hope, like the Castor family, that he is out there somewhere and if he is, maybe he is reading in the media that his father has passed."

Detective Senior Sergeant Asenjo said Mr Castor's death was a "sad tale" for a family desperate for answers.

"Rolf and I would email each other every couple of months. He made a Facebook page asking for information about Max and when he received updates he would provide it to me and I'd conduct any investigations we could to rule information out as a possibility or establish the veracity of that report," he said.

"We would also engage with the Castor family every year through Missing Person's Month, to get their approval to publicise the fact that Max, a young man in the prime of his life, had gone missing."

Through the constant email exchanges, the detective said he felt like he got to know Mr Castor well.

"He was a loving father, not just to Max, but to all of his kids, and I can see that Max's disappearance weighed down heavily on him," he said.

Detective Senior Sergeant Asenjo said he and Mr Castor would often exchange photographs of their homes.

"I would take photos of the Port Campbell area, hopefully to help him feel a little bit more connected to his son and to the part of the world that Max really loved," he said.

"I'd send him photos of Australia, at its finest in summer months, and he would send me a near identical photo in Sweden during winter.

"I felt like it was a warm relationship between the two of us with a common goal to try and locate his son."

Detective Senior Sergeant Asenjo said he had not given up in his search for Max and urged anyone with information to come forward.

"Hopefully he is reading this and I encourage Max, and anyone who knows his whereabouts, to get in contact with us so we can provide some closure to the family," he said.

Anyone with information should contact Warrnambool police or Crime Stoppers.

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