Officers arrested an 18-year-old suspected of plotting the attack in a dramatic swoop at the port of Dover on Saturday. The teen - who is being held at a London police station - is thought to have been a 'problematic foster child' who was allegedly arrested two weeks ago near to where the attack took place before being freed. If true, this appears to suggest that President Donald Trump's much criticized tweet revealing the suspect was known to British law enforcement was not entirely wrong.