What the police have collected quite seamlessly in recent years is a timeline of CBs stays. (link is below)
The 11-year-old girl was murdered in Grevenbroich in 1996.
In 1995 (CB was 19 years old) he fled from Germany to Portugal to escape a juvenile sentence.
In 1999 he was arrested there with a European arrest warrant and transferred to Germany.
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It is possible that he also returned to Germany once during this period. But why to Grevenbroich? Nobody goes there "just by the way"! CB has no social reference points there (according to the current state of knowledge), there is no matching DNA.
If the police exclude the case in connection with CB, they will have good reasons. Because one thing is clear: They want to nail him!
CB timeline (in German)
https://www.allmystery.de/dateien/rjkcxgxnpafv_Zeitachse_-_Christian_B_Fall_Maddie.pdf