SEDALIA, Colo. -- A freight train car came loose Wednesday and killed an employee doing track work as it raced 32 miles before it was stopped in a Denver rail yard, officials said.

The car broke away from a Burlington Northern Santa Fe Railway work train near Castle Rock and hit grinder operator Thomas Durst, 36, near Sedalia, about five miles from Castle Rock, company spokeswoman Lena Kent said.

The car, a low-sided, open-topped car known as a gondola, was stopped near Burlington Northern Santa Fe's Denver rail yard after it was diverted to an uphill track, Kent said.

The train traveled northbound on the southbound tracks shared by Burlington Northern and Union Pacific railroads. Kent said it was not known how fast the car was going.

The Federal Railroad Administration is investigating.