Belarus plane grounding

So you all must know this story. Roman Protasevich was arrested after the plane was grounded in Belarus and the Russian government captured him. Now he's a political prisoner but my point is if he was such a big problem then why didn't they arrest him ages ago and secondly a recent political prisoner died in prison so why is all their prisoners dying why are they so scared of letting these people live. It's so strange why the media don't pick up on this.