Investigators believe a 1,200-foot cargo ship dragging anchor in rough seas caught an underwater oil pipeline and pulled it across the seafloor, months before a leak from the line fouled the Southern California coastline with crude. A team of federal investigators trying to chase down the cause of the spill, boarded the Panama-registered MSC DANIT just hours after the massive ship arrived this weekend off the Port of Long Beach, the same area where the leak was discovered in early October. During a prior visit by the ship during a heavy storm in January, investigators believe its anchor dragged for an unknown distance before striking the 16-inch steel pipe, Coast Guard Lt. j.g. SondraKay Kneen said Sunday. The impact would have knocked an inch-thick concrete casing off the pipe and pulled it more than 100 feet, bending but not breaking the line, Kneen said. Still undetermined is whether the impact …