I mean, maybe they do have more withheld evidence? That's certainly possible. But my gut instinct (which of course has no bearing on anything since I know nothing!), based on what's been said/released, is that while MM is important to the investigation in terms of CB's possible involvement in her disappearance, she's also 'peripheral' to it in that they now may have ample other unrelated evidence of criminal activity involving other people to charge him with.
There's also a lot of me that doesn't want the repulsive CB to have had anything to do with MM's disappearance, for that little child's sake.
As the first infos of the investigation by german L.E., especially HCW were made public, his former lawyers quit their mandate without giving a reason, what is remarkable. It is possible, that CB told them a lot, what maybe come to light and that maybe to big for them to handle. They are just pretty young lawyers so far.
Then, FF and JS took the case as lawyers, for what reason so ever. Even JS is known for being pretty offensive against LE, but you hear nothing from him. Maybe due to tactical reasons, maybe due to let the investigations come forward. The way FF talks to the press, i never heard or mentioned a "My client is innocent!". He acts very careful.
In my opinion, they both know more because he opened some truth to the lawyers. To remain silent until there are concrete accusations is a tactic, that is often done, if you can't rule the verdict out by yourself. It is a defensive strategy, not an offensive one, that is often much better to follow, if your "vest is clean". And a non-existing-statement from "star-lawyer" JS is not the way, the lawyer treated his cases in the past.
There must be something. Being like CB is supposed to be, could also be a huge burden and he and his lawyers know, that his life will never be like before. Even if they could not charge him.
MN was brought to confession, without forensic evidence that could be linked to him without a reasonable doubt to him, by the way!