Fatal Explosion Caused by Gas Leak.

July 27, 2012 Updated Jul 27, 2012 at 7:09 PM EDT

By Ed Reilly

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July 27, 2012 Updated Jul 27, 2012 at 7:09 PM EDT

TOWN OF WILSON, N.Y (WKBW) Niagara County Sheriff James Voutour announced that investigators are "confident" that a propane gas leak caused a devastating explosion that killed a teenage girl and injured four members of her family.

Investigators are now trying to figure out what caused the propane to explode, and they are examining various appliances.

"We are very confident that somehow there was a leak that allowed propane gas to fill the house, and because it is heavier, it will generally seep to the basement area of the house," said Sheriff Voutour.

14-year old Sarah Johnson was killed in the blast that destroyed the Johnson family home on Chestnut Road in the Town of Wilson early Tuesday morning.

Her parents, Jody and Judy Johnson, along with siblings, Nathan and Katie, were thrown from the exploding house and taken to the Erie County Medical Center (ECMC).

Jody and Nathan Johnson were released on Thursday.

Judy Johnson has been upgraded to 'good' condition.

Katie Johnson still remains in critical condition after suffering severe burns.

The family's pastor, Bill Lowery, Jr, says the family is postponing a funeral for Sarah until their daughter Katie is able to take part.

However, there are plans to hold a "service of healing" for the family and the community after Judy Johnson is discharged from ECMC.

Pastor Lowery saying the time and place are still being finalized.