The libertarian Murray N. Rothbard said that it would be wrong to kill someone for stealing a pack of gum. If you steal gum, this is an act of violence against the property owner. The owner has a right to use defensive violence to get the gum back, but killing the thief goes too far. That is too much force because it is not equal to the force used by the thief. Punishment must be equal to the crime. A student and colleague of his, Walter Block, said that a punishment should not be equal to the crime, but rather enough to make up for the damage the crime caused plus how much it cost to catch the criminal.