NorthWestern Energy says an investigation has found that a separation on a 2-inch natural gas service line caused an explosion in downtown Bozeman that leveled four buildings and killed a woman who worked at an art gallery.

The investigation was conducted by the Bozeman Fire Department and the U.S. Department of Alcohol, Tobacco and Firearms.

Bozeman Fire Chief Jason Shrauger says the leak occurred in a service line between the main gas line and the meter for Montana Trails Gallery.

The explosion crumbled four buildings, destroying Boodles restaurant, Montana Trails Gallery, LillyLu`s children`s store, Tolstedt Architects and the American Legion Hall. Several other businesses were suffered significant damage, including the Rocking R Bar, the Pickle Barrel restaurant inside the Rocking R, the Rocky Mountain Rug Gallery and Starky`s Authentic Delicatessen.

Tara Reistad Bowman, 36, died in the blast.