JEFFERSONVILLE, Ind. (AP) — Fire investigators have determined the explosion of a southern Indiana house over the weekend that left one dead was caused by natural gas.

Fifty-year-old William Phillips was killed when a home exploded Sunday in the Ohio River city of Jeffersonville. His wife, Janet Phillips, remains in critical condition at University of Louisville Hospital.

Investigators for the Jeffersonville Fire Department announced that 12 hours before the explosion, an increased amount of gas was spilling into the home. The gas was ignited by an unknown source.

Gas supplier Vectren says the source of the gas was not a pipeline or infrastructure owned by the utility. Vectren said it is conducting its own investigation of the explosion.

A woman in a neighboring home was also injured by the explosion that damaged 20 other homes. An 11-year-old girl suffered a broken collarbone.