The disappearance of German tourist Lars Mittank is one of the most baffling cases and still plagues his family and authorities.
While there are hundreds of ongoing missing persons cases, Lars' is peculiar because CCTV cameras captured the strange last moments before he went missing.
Mittank was on a group holiday in Golden Sands, Bulgaria and a week after they arrived, the then 28-year-old got into a fight with four blokes over football. During the brawl, he suffered a perforated ear drum, which prevented him from flying home with his mates.
While they were happy to stay with him until he was fit to fly, he assured them that he was fine and would take his prescribed antibiotics and come home later.
Lars checked into a cheap hotel and that's where his odd behaviour started.
Credit: Find Lars Mittank/Facebook
His mum says she received frantic messages from him saying four men were following him, asking her what his pills were and then she should cancel his credit card.
The Mirror says cameras captured Lars pacing about the hotel lobby as well as hiding in an elevator. He left the building around 1am however no details have emerged about where he went or what he did.
The following day he went to Varna Airport to fly home and sent his mum a message saying he'd be departing soon.
But before he could get on the plane, he reportedly had to be checked over by an airport doctor about whether his ear would withstand the journey. Dr Kosta Kostov, who examined Lars, recalled the German tourist started to freak out and at one point said: "I don't want to die here. I have to get out of here."
Credit: Lars Mittank/Facebook
Cameras at the airport filmed the last time he was seen alive and the footage is strange to say the least. It shows Lars sprinting inside the building, slowing to a light jog once outside before he hopped over a fence and disappeared into a nearby forest.
Authorities are at a lost as to what caused him to suddenly run from the airport and in the four years since his disappearance, there's been no sight of Lars.
His family's hopes were raised when a man matching Mittank's appearance was discovered in Brazil - however doctors confirmed it wasn't Lars when his blood type and eye colour didn't match up.
That man ended up being from Canada who had been missing since 2012.
Featured Image Credit: Varna Airport/Lars Mittank