By Ian Simpson WASHINGTON (Reuters) - An alleged al Qaeda-backed plot to derail a U.S. passenger train in Canada sought to exploit the vulnerabilities of railroads that have not gotten much attention from the American public. While the United States has sharply tightened security around airlines since the September 11, 2001, attacks, trains are far harder to police, with masses of passengers getting on and off and stops at many stations on a single line. Thousands of miles (km) of track, bridges and tunnels present a major challenge to monitor. ...

By Tim Gaynor WEST, Texas (Reuters) - A rail car filled with extremely hazardous ammonium nitrate did not cause the fiery explosion at a Texas fertilizer plant, investigators said on Tuesday, in their first statement ruling out possible sources of the deadly blast six days ago. Fourteen people died in the explosion at the West Fertilizer Co last Wednesday, and some 200 were injured. Investigators said they also ruled out a weather event such as lightning as the cause of the fire and blast, and said they had narrowed down the possible sources to an accident, arson or an unexplained cause. ...