Investigators have determined that the cause of a house fire in Ukiah this past Sunday night was arson. Analysis of the scene proved that the fire was deliberately set . The house on Porizio Lane was unoccupied at the time and investigators say it looks like squatters had taken residence. According to MendoFever, Battalion Chief Buckingham said the residence has had issues with squatters in the past, and the fire was not the result of an unattended cooking or warming fire.