FORT WAYNE, Ind. (WANE) — Authorities investigating an April fire at a north Fort Wayne mobile home that killed four children have been unable to determine what sparked the blaze.

The Allen County Coroner’s Office said Wednesday that the Indiana State Fire Marshal’s Office said the amount of damage from the fire at the mobile home along Grassy Lane in the Dupont Estates community made it impossible to prove a definitive cause “to an acceptable level of certainty.”

As a result, the coroner’s office said the manner of the deaths of 10-year-old Matthew Damron, 5-year-old Johnnie Mann-Goff, 3-year-old Jefferson Goff, and 2-year-old Rosalynn Goff have been ruled “undetermined.” All four children died of smoke inhalation and thermal burns, the coroner’s office ruled previously.

It was around 8:30 a.m. April 21 when flames consumed the mobile home. Firefighters had the blaze under control in 23 minutes, but four children were found dead inside the destroyed home.

Four adults were able to escape the fire, and were hospitalized.

The mobile home was destroyed, with heavy fire, water and smoke damage, the report said.

According to the state fire marshal, the fire was believed to have started “in or around the area of a recliner” based on evidence gathered during the investigation.