The state fire marshal has closed its investigation of a house fire that killed two children in southern Minnesota last December.

The state fire marshal has closed its investigation of a house fire that killed two children in southern Minnesota last December.

The cause of the fire at a farm in Redwood County will remain undetermined.

Seven-year-old Hazel Thooft and 4-year-old Isiah Thooft died in the fire last December in Lucan. KARE-TV reports investigators haven't ruled out two possibilities for the fire — faulty electrical equipment connected to a Christmas tree and a child playing with some sort of ignition source.