From JC's book, p404 to p405:
He also admitted that the first tip on Brueckner had come into the BKA police department in 2013 and, in retrospect, it could have been handled better. ‘I only know it was a tip off from the UK without any details,’ explained Wolters. ‘There was no concrete reason or suspicion. No-one said how he might be involved. It was just; “take a look at Christian B.” So, the British police didn’t know anything. They just thought, “What is this? Who is this?” In Germany there was no investigation at the time into Christian B and because the BKA didn’t know Christian B, they gave it to the Braunschweig Police department, and they then spoke with him as a witness and they only asked him a few questions. And basically he answered the questions and did not seem suspicious, so they sent the information to the BKA, and the BKA sent this to the British police. And then nothing happened.’ When pressed on why they hadn’t done a bit of probing first, cross-checking with his previous record, other federal regions of Germany or other European countries, he skirted around it. ‘Look, we had no concrete evidence, nothing to go on, so we had to approach him in a very open way and write to him to tell him what it was about,’ he said. ‘And he insisted he had nothing to do with the crime and so that was that, done and dusted. Because one couldn’t hold anything against him. One could not confront him with any findings. ‘Looking at it today, with hindsight yes it was unfortunate, but at the time we didn’t have any knowledge.’
This is the point I was making the other day. Profiling only takes you so far.
The perp may be included in your long list - but unless you have something specific to tie the perp to the case you are still stuck. Limited powers to question. Can't get a search warrant without cause. Yes he had a record, but frequently the perps in these cases have no record.
Profiling is an important tool that can help you narrow down the field or find potential suspects - but if you can't then find any evidence, chances are your theory is wrong. This has always been the biggest problem in the case. As far as we know, the focus on the abduction theory never generated any solid evidence until 10 years later.
I think people also forget that the dozens of potential suspects have been IDed in this case over the years.