It’s not complex at all. If they had concrete evidence of his guilt they would have charged him. It’s actually very simple and I’ll predict he’ll never be charged.
The situation is probably more complex than it seems.
For argument’s sake, suppose the German police unearthed a memory stick containing images of a man who appeared to CB shooting a child who looked uncannily like Madeleine. The images, uploaded onto said memory stick, originated from a phone police are almost sure was used by the suspect at the time but proof is needed.
AFAIK a person cannot be prosecuted using images alone where identification & crime cannot be 100% proven. The police have a suspect in a probable crime but no known crime scene, body or murder weapon to assist the investigation. Furthermore, they have no forensic evidence linking the suspect to the apartment from which the child was taken. The child may even have been delivered to the suspect by another party, a gun held to his head & an order issued to shoot the child whilst being filmed by A N Other. We just don't know until the Germans complete their investigation then question the suspect.
All my opinion.