Lockport, NY (WBEN) Niagara County Sheriff Jim Voutour says a propane leak and a spark led to Tuesday's deadly house explosion in the town of Wilson. 14 year old Sarah Johnson died in the blast.

"We're quite confident that there was a build up of propane gas in the house," Voutour said during a Friday afternoon news conference at the Niagara County Sheriff's Office.

However, Voutour says it's unclear what caused the spark that led to the explosion. Investigators say it's unclear how long the propane leak had lasted. They say it could have been an appliance, but the probe continues.

"The propane will not explode on its own. It takes some type of ignition, and that could come from any number of appliances or devices that are in the house.

Johnson's father, Jody, and brother, Nathan, were released from ECMC on Thursday. Judy Johnson is in fair condition at ECMC, and Katie remains in critical condition in the facility's burn unit.

Rev. Bill Lowery, Jr, the family pastor at the Ransomville Free Methodist Church, says the Johnson family wants to thank the community, and he is confident they are in a healthy place. There are plans for a public "service of healing" for Sarah Johnson, but no date or place has been established yet. 

The family will also have its private service for Sarah in due time.

Investigators cleared the scene on Wednesday, and now an insurance company has secured the scene for its own investigation.