EVANSVILLE, Ind. (AP) — Authorities worked Thursday to determine the cause of a house explosion in a southern Indiana neighborhood that killed three people and left another person hospitalized.

The explosion Wednesday afternoon in Evansville damaged 39 homes and crews had not yet completed thorough searches of all of them due to instability of the structures, Fire Chief Mike Connelly told reporters Thursday morning.

Eleven of the damaged homes were uninhabitable and will have to be demolished, Connelly said, and finding a cause is expected to be a “very tedious process — and lengthy.”

Names of the dead hadn’t been released as of Thursday morning. Injuries to the fourth victim weren’t considered life-threatening, Connelly said.

The Bureau of Alcohol, Tobacco, Firearms and Explosives also was investigating.

Evansville is located along Indiana’s border with Kentucky. The blast left debris strewn over a 100-foot (30-meter) radius. Debris included construction materials like wooden boards, window glass and insulation.

CenterPoint Energy, the local gas utility, was last called to the home in January 2018, Connelly said Wednesday.

“CenterPoint Energy is working closely with the Evansville Fire Department, State Fire Marshal and other agencies as the investigation of this incident continues,” the utility said.

It was the second house explosion in the area in just over five years. A house explosion on June 27, 2017, killed two people and injured three others.

Wednesday’s explosion also brought to mind a massive blast in 2012 that destroyed or damaged more than 80 homes on Indianapolis’ south side and killed two people. A man was convicted of tampering with a natural gas line at his then-girlfriend’s home in an attempt to commit insurance fraud.