Arson is a crime where a person sets fire to a building for financial gain.
Often it is the owner looking for an insurance payout who sets fire to their building.
But it can be someone else who is promised a pay-off from the owner who sets fire to the building.
The person who sets fire to the building must hide the fact that they caused the fire. They must make it look like the cause is an electrical spark or arcing in old wiring, or a heat source such as a heater. The fire must spread quickly and destroy the building so that it is not easy to determine the cause.
In all cases, the best evidence is direct - someone sees them 'in the act' or the person boasts later about how they started the fire.
But if there is no direct evidence, then circumstantial evidence must be overwhelming to convict a person 'beyond reasonable doubt'.
This was the situation that two arsonists faced in the NSW Court of Criminal Appeal recently.