^Don't fool yourself. Someone tried to assassinate ou elected premier on Election Day 2012(and murdered a stage technician in the process).
In any case, according to the latest details, Mohamed isn't a suspect after all, just an important witness. Alexandre is known to frequently post alt-right stuff on social media.
Update: Mohamed has been released. Turns out he's actually closer to a hero than a terrorist. Immediately after the shooting, he came back inside the Mosque to give first aid to the victims, but when the police finally arrived he didn't realize they were police officers. He saw their guns, got scared and tried to run away, so they arrested him by mistake.