Complex sentence: On arrival in Paris, Paco, international terrorist, was arrested, while his mistress Laura joined his accomplices: they all belong to terrorist and anarchist splinter group, Ravachol-Kropotkin, led by Paco.
Split into simpler sentences: On arrival in Paris, Paco, an international terrorist, is arrested, while his mistress Laura joins his accomplices. They all belong to terrorist and anarchist splinter group, Ravachol-Kropotkin, led by Paco.