In order to act as a deterrent, executions must be effective.
In order to be effective, executions must be:
Swift and certain.
Broadcast to the population.
~ Swift and certain executions might also lead to an abuse of civil rights which, in turn, would lead to an increase in the number of innocent people being executed.
~ We would have to implement televised executions. An execution done in secret does not have a deterring effect.