On 15 April 2013, two bombs exploded at the finishing line of the Boston Marathon.
Just over a month later a British soldier was run over and hacked to death on a London street.
The images from either side of the Atlantic shocked the world.
With access to exclusive interviews and behind-the-scenes filming of the parents of the Boston bombers, Matt Frei investigates whether the two attacks mark a new chapter in the battle against terrorism.
