OK - sanity check
There is literally nothing to link the cases of IG and MM that we know of
When police identify this kind of offender, it makes sense to check other cold cases that could be linked if evidence is discovered. So for example the case of HB could be linked by actual evidence - the investigative breakthrough coming from similarities in the MO and the witness.
So as we know they checked IG, but IIRC it has also been said there is no reason to believe it has anything to do with CB.
Mere proximity, like "profile" is not evidence. And I'd also dispute, in the german context, that 50km is proximate. In my case, 50km includes a major metro with millions of people, and multiple towns with tens of thousands of people.
This is my issue with these theories being promoted by journalists. We haven't seen any evidence CB killed anyone let alone 3 people. Did he? I have no idea. But such allegations need to be made by authorities, not by people engaging in wild speculation on podcasts.