From: http://www.bbc.co.uk/ethics/capitalpunishment
(Here the text for the final exam, as agreed. Please note that this is an edited version, which means that I have made some changes. The words marked in red are probably new terms for you which you should check during your preparation for the final exam; it is important that you understand them)
Value of human life
Everyone thinks human life is valuable. Some of those against capital punishment believe that human life is so valuable that even the worst murderers should not be deprived of the value of their lives.
They believe that the value of the offender's life cannot be destroyed by the offender's bad conduct - even if they have killed someone.
Some abolitionists don't go that far. They say that life should be preserved unless there is a very good reason not to, and that those who are in favor of capital punishment are the ones who have to justify their position.
Right to live
Everyone has an inalienable human right to life, even those who commit murder; sentencing a person to death and executing them violates that right.
This is very similar to the 'value of life' argument, but approached from the perspective of human rights.
The counter-argument is that a person can, by their actions, forfeit human rights, and that murderers forfeit their right to life.
Another example will make this clear - a person forfeits their right to life if they start a murderous attack and the only way the victim can save their own life is by killing the attacker.
Execution of the innocent
The most common and most cogent argument against capital punishment is that sooner or later, innocent people will get killed, because of mistakes or flaws in the justice system.
Witnesses, (where they are part of the process), prosecutors and jurors can all make mistakes. When this is coupled with flaws in the system it is inevitable that innocent people will be convicted of crimes. Where