By EILEEN SULLIVAN Medical workers aid an injured man at the finish line of the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. Two bombs exploded near the finish of the Boston Marathon on Monday, killing two people, injuring 22 others and sending authorities rushing to aid wounded spectators, race organizers and police said. (AP Photo/Charles Krupa) WASHINGTON (AP) — A law enforcement official says cellphone service has been shut down in the Boston area to prevent any potential remote detonations of explosives. Authorities have not identified what caused the explosives that erupted at the finish line of the Boston Marathon. The official was speaking on condition of anonymity because the investigation was ongoing. The explosions have killed two people and injured at least 23 others.