Ali Mohammed Said, of north London, was arrested as he tried to travel to Belgium with a fake passport; he is accused of seeking to help C.F., a terrorist with international connections, travel to Syria to join the Islamic State. Scotland’s top prosecutor, who is continuing to investigate the 1988 Lockerbie bombing, said his team is working with officials from the US and the UK to bring to justice those who acted along with Abdelbaset al-Megrahi.