The important word is "if". Where there is suspicion there should, of course be investigation. What there should not be is prejudicial statements by the authorities prior to any trial. Everyone is entitled to the legal protection which is available to prevent them being declared guilty before being arrested whatever their background.
The idea that lay persons can affect an investigation is a bit fanciful imo.
Amaral obviously does not believe that - he certainly did his damnedest to have an adverse effect on the German investigation starting with his announcement to the world regarding the perfect patsy but for the fact he wasn't dead - using Saunokonoko's podcast as his vehicle.
Neither are individuals hiding their light under a bushel when it comes to negativity regarding the investigation aimed at solving what happened to Madeleine McCann. So weird from people who pay lip service to "justice" for Madeleine but who have spent fifteen years fighting tooth and nail to prevent just that.