Looting is often opportunistic. The apparent lapse in authority enables people to believe that they won't be discovered or charged. Looting also cascades through a group of people as one person believes that his contribution to the crime is lessened because someone else is looting, too. People may also believe that if the goods are not stolen, then they will simply be wasted, and see their act as a lesser of two evils. Finally, a looter may believe that if he doesn't steal the property, it will simply be stolen by someone else and he will gain nothing from his obedience. Looters are usually locals of the site of the disaster, and as such, may have lost a lot of their own property. This further encourages them to steal as it is reducing the negative impact of the disaster.
In many countries, even in Western democracies that otherwise ban the death penalty, extraordinary measures may be taken against looters, during times of crisis. Looters may be summarily shot by the police, army, or property owners. Extraordinary measures, combined with an impressive show of force, help to discourage looting and to disperse crowds that would now find a normal show of force non-threatening. This is also common police practice in discouraging potential riots, which are often associated with looting, from escalating.
The shooting of looters is also to prevent further damage to the economy.
(Excerpt from Wikipedia: 31 Aug 2005)