but there is no case against them built from electronic surveillance because they arnt doing anything illegal there just discussing their ideology.
which is why we need to just stop them from entering in the first place - whether the EU or the UK
in the case of the UK the home secretary is happy to use her powers and ban say an american pick up artist because he's offensive to women yet foreigners with questionable views on jews, jihad, gays etc.. have been documented as having spoken at mosques & universities in the UK
frankly if they're 'known' to the intelligence services as this Moroccan was then just ban them, you don't need to build a case they're foreigners, they've got no inherent right to be here. Granted if someone really really wanted to get into the EU via a backdoor route then they could perhaps find a way but it does make things much much harder for them to be able to pull off stuff like this