On a straight legal view, there is no connection between MN's french case/trial about Jonathan C. and the CB- related MM-case, as long as CB didn't take part in the murder of Jonathan C.. But if a suspect has been extradited, it would be a huge and expensive effort to extradite over and back for these 8 Months. But it's not a problem for german authorities to interrogate MN on other cases in a french prison so far. That's what BKA is responsible of. If CB is needed as a witness in another trial, he would be taken to court for a few days, right. If prosecuters see any involvement, they would likely wait until the french trial has been finished.