Nebraska authorities say a fatal fire last month that killed an 8-year-old boy and his grandmother was not criminal.

The Nebraska Fire Marshal says the Feb. 23 mobile home fire in Bellevue was caused by either combustible material that came in contact with a space heater or electrical wiring problems.

Authorities have not released the victims’ names pending DNA results. But family identified them as Sandy Nielsen and Devin Nielsen.

Three others escaped the fire and were transported to a hospital. They later were treated and released.