Authorities say a fire that killed a woman and her grandson in a small eastern Missouri town is now a homicide investigation.

The fire on Dec. 7 in Cadet killed 11-year-old Trevor Cook and 53-year-old Tammy Thurmond Feverston. Washington County Sheriff Zach Jacobsen said Sunday the case was being classified as a homicide. He did not provide further details.

The Mineral Area Major Case Squad has been activated to investigate the case. The Potosi firefighters found a home fully engulfed in flames when they arrived in the house in Cadet, an unincorporated town in Washington County.

Heavy flames prolonged the time it took firefighters to find the victims.