A member of the National Guard and a Boston policeman direct a man away from a barricade near the finish line of the Boston Marathon in Boston Tuesday, April 16, 2013. The bombs that ripped through the Boston Marathon crowd were fashioned out of ordinary kitchen pressure cookers, packed with nails and other fiendishly lethal shrapnel, and hidden in duffel bags left on the ground, people close to the investigation said Tuesday. (AP Photo/Winslow Townson)A marathon path runs 26.2 miles along an open street. So Much tougher to secure than an arena with doors and partitions.