PUEBLO, Colo. -- Joint task force investigators announced Thursday that an explosion that killed a Pueblo woman and injured seven others was caused by a natural gas leak from a pipeline under the street.

Pueblo fire department spokesman Woody Percival said 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 the chemical additive that gives natural gas a distinctive rotten egg smell was likely filtered or altered, making the odor unrecognizable when it got to the basement and ignited.

Percival said the gas could have been ignited by anything -- pilot lights on gas-operated appliances or candles that were recently placed atop tables in the dining room.

"There are so many (potential) ignition points that we may never know," he said.

Ashley R. Johnson, 22, was killed and seven people were injured in the blast and subsequent fire. The Branch Inn restaurant and a neighboring store, Classic Boutique, were destroyed.

The explosion was categorized as "accidental in nature." The task force looking into the cause of the explosion was made up of local, state and federal investigators.

The announcement came a week after the Nov. 13 explosion leveled the Branch Inn and A Classic Boutique on the corner of C Street and Union Avenue, and hours before a memorial service for Johnson.

Johnson's funeral is scheduled for 1 p.m. in Pueblo.

Two of the victims injured in last week's blast remained hospitalized at Parkview Medical Center.

Frank Vigil, 41, co-owner of the Branch, was listed in fair condition; and patron Eugene "Geno" Roney, 74, was listed in serious condition.