PUEBLO, Colo. — Investigators have determined that a natural gas leak from a pipeline under the street led to a deadly explosion that leveled a restaurant and a neighboring store.

Pueblo fire department spokesman Woody Percival says the gas "took the path of least resistance" and passed through the soil, building up in the Branch Inn's basement.

Restaurant staff smelled an odor but assumed it was sewer gas. Percival said Thursday the chemical additive that gives natural gas a rotten egg smell was likely filtered or altered, making the odor unrecognizable when it got to the basement and ignited.

Twenty-two-year-old Ashley R. Johnson was killed and seven people were injured in the Nov. 13 blast. A Classic Boutique was also destroyed.