Evansville, IN – A leaking gas line caused the accidental explosion that killed three people and damaged nearly 40 homes in August in Evansville, Indiana, the state Department of Homeland Security said Wednesday.

Investigators found the uncapped line’s valve in the open position in the basement of a home determined to be the epicenter of the explosion, according to the statement from state DHS.

Meter data showed an increase in gas usage in the two days before the explosion, the statement said.

The ignition source could not be determined, the statement said.

A pressure test on the gas lines between the main and meter showed them to be working properly. Investigators could not determine how the people in the home did not notice the gas accumulating, according to the statement.

The three people who died were identified at the time as 43-year-old Charles Hite, 37-year-old Martina Hite, and 29-year-old Jessica Teague, according to the Vanderburgh County Coroner.

Charles and Martina Hite had been married about three years, according to a relative.

Fire officials said at the time that 39 houses sustained severe to minor damage during the explosion.

Evansville is about a three-hours’ drive southwest of Indianapolis.