Autopsies on a brother and sister from St. Clair County who were killed during a bonfire explosion show that the two died from blunt force trauma to their bodies and not burns.

St. Clair County Medical Examiner Dr. Daniel Spitz said Tuesday that 18-year-old Savannah Blewett was killed by trauma to her head and face. Her brother, 27-year-old Christopher Blewett, suffered deadly trauma to his chest.

The two were killed Saturday when a gasoline-drenched bonfire, which was part of Savannah's graduation party, exploded at about 9:30 p.m. at her brother's home on Gratiot Road in St. Clair Township.

Witnesses told deputies the man drenched the bonfire in gasoline, then invited his sister to set it afire.

St. Clair County Sheriff Tim Donnellon says "it was mean to be a celebration that went terribly wrong."

Donnellon said the investigation determined that simply too much gasoline had been put on the wood before it was ignited and no criminal intent was found.

At least four other people were hurt, but are expected to be OK.

Funeral arrangements for the siblings have not yet been released. But their bodies were released to the Henry Malburg Funeral Home.