The prime suspect in the Madeleine McCann case is feared to have committed numerous sex offences on regular trips across Europe as he drove between Germany and Portugal for more than two decades.
Christian Bruckner (43) is known to have frequently driven the 1,600 miles between his native Bavaria and the Algarve, through France and Spain and possibly Switzerland and Belgium.
It is feared the convicted rapist, burglar and drug dealer could have used the trip, which would have taken more than a day, to scout for victims.
The full extent of his nomadic lifestyle has meant he either lived in, or had been jailed for crimes in, countries including Germany, Italy and Portugal.
"He would never be able to put down roots because ultimately his sexual fantasies would have to come to the fore. When that happens, there would have been a lot of gossip which would have meant he would have to move on," said David Wilson, an emeritus professor of criminology at Birmingham City University.
"It's absolutely right to think he would have offended in those places he moved, whether in Germany, Portugal, or anywhere in between."
In 1995, aged 18, Bruckner first travelled to the Algarve. He was escaping from part of a two-year youth court sentence for sexually assaulting two children, a boy and a girl.
A year after Bruckner arrived in the Algarve, Rene Hasee, from Elsdorf, Germany, disappeared on June 21, 1996, while on holiday in Aljezur, 25 miles from Praia da Luz.
His parents lost sight of him after he ran ahead on the beach. On the sands where the six-year-old boy had been lay some of his clothes. Last week , German detectives said they were looking again into his disappearance.
The northerly route between Bruckner's native Germany and Portugal could take him within miles of the Belgian seaside resort of De Haan. In the summer of 1996, 16-year-old Carola Titze went for a morning walk along the beach while on holiday there. She never returned, and her body was found six days later.
The schoolgirl was reported to have been in contact with a German man whom she was seen with at a disco in the days before her murder.
Yesterday, the public prosecutor's office in Bruges confirmed it was investigating whether Bruckner could have played any part in her death.
If Bruckner had tried to forge a new identity he failed. In 1999, he was extradited from Portugal to Germany to face the courts for previous juvenile crimes. He had earlier been jailed for a series of burglaries on the Algarve.
Nonetheless, a few years later he was back in Portugal and moved into a rundown property where neighbours reported seeing a variety of dishevelled cars parked up.
By the summer of 2007, his life was truly mobile after he resorted to living in a VW camper van, probably with his unnamed English girlfriend (he was fluent in English). When Gerry and Kate McCann, along with Madeleine and their twins, arrived in Praia da Luz, he was known to have been trundling around the area.
An hour before the three-year-old vanished, Bruckner received a 30-minute call in the town. The next day, he arranged for the ownership of his German-registered Jaguar to be transferred to another person's name back in Germany. He and his girlfriend split up and he returned to his homeland.
In May 2015, Inga Gehricke (5) disappeared in a case so similar to what happened in Praia da Luz that she became known as "the German Maddie". She vanished from a family barbecue after going to collect firewood in the northern town of Stendal. She has never been seen since.
As was the case in the McCann inquiry, Bruckner became a suspect in the Gehricke case, but faded from the inquiry, despite it being claimed he had been at a service station only 90 minutes away from the scene.
A raid in 2016 on his property uncovered a Skype chat on a computer in which he stated he wanted to "catch something small and use it for days".
According to Bild magazine, a USB stick found at the site where he lived had images of the abuse of babies.
It is clear that Bruckner was reluctant to sever links with Portugal. Although he regarded the Algarve as his main home for 12 years from 1995 to 2007, one of his former landlords in Bavaria said he was regularly returning to Portugal in the years before his arrest in 2018.