SAVANNAH, Ga. — Don Varnadoe spent months watching videos about train trips on his office computer in preparation for a special cross-country vacation to celebrate his and Margie Varnadoe’s 50th wedding anniversary.

The couple died when an Amtrak train they were on derailed in rural Montana.

They were among three people who died along with a 28-year-old Illinois man named Zachariah Schneider, according to the Liberty County Sheriff’s Office in Montana. Schneider was traveling to Oregon with his wife, Rebecca Schneider, who survived and filed a lawsuit Tuesday against Amtrak and BNSF Railway.

The Amtrak train was going just under the speed limit at about 75 mph when it went off the track along a gradual curve, possibly ejecting passengers, U.S. investigators said Monday. The Amtrak Empire Builder that was en route from Chicago to Seattle crashed Saturday afternoon near Joplin, a town of about 200 near the Canadian border.

The train, carrying 141 passengers and 16 crew members, had two locomotives and 10 cars.

Investigators are studying video from the train and another locomotive that went over the same track a little over an hour earlier, National Transportation Safety Board Vice Chairman Bruce Landsberg said Monday. The derailed train also had a black box that records everything happening in the train, he said.