A Federal Express tractor-trailer wrecked this afternoon on Interstate 270 in St. Louis, caught fire and exploded, initially prompting worries about a terrorist attack. Authorities have ruled since that it was simply an accident. The driver and a passenger in the cab of the truck walked away unharmed. Captain Chris Ricks with the State Highway Patrol says authorities first feared the trailer full of packages had exploded, which prompted speculation that it was a terrorist incident. The investigation though has concluded the driver attempted to swerve around a car that had cut in front of him, the truck hit a guard rail that ripped open one of the trailers, spilling packages across I-270. The gas tank then ignited and blew up. Authorities on the scene notified the governor, state homeland security officials and even the White House before it was determined not to be a terrorist incident, merely an accident.