By Jacinda Valeontis, Amnesty International Australia online team

Killers, murderers, terrorists, drug lords. Who cares if they are faced with death, right? These are the arguments of many pro-death penalty advocates who highlight the guilt of the convicted and the serious nature of their crime.

But what if you couldn't be sure? What if it wasn't only reserved for the "worst of the worst"? World Day Against the Death Penalty reminds us all to challenge the notion of "an eye for an eye" equals justice.

Here are five reasons why:

1. You can't take it back

The death penalty is irreversible. Absolute judgments may lead to people paying for crimes they did not commit. Texas man Cameron Todd Willingham, for example, was found innocent after his 2004 execution.

2. It doesn't deter criminals

In fact, evidence startlingly reveals the opposite! Twenty seven years after abolishing the death penalty, Canada saw a 44 per cent drop in murders across the country. And it wasn't alone.

3. There's no 'humane' way to kill

The 2006 execution of Angel Nieves Diaz, by a so-called 'humane' lethal injection, took 34 minutes and required two doses. Other methods of execution used around the world include hanging, shooting and beheading. The nature of these deaths only continues to perpetuate the cycle of violence and does not alleviate the pain already suffered by the victims’ family.

4. It makes a public spectacle of an individual's death

Executions are often undertaken in an extremely public manner, with public hangings in Iran or live broadcasts of lethal injections in the US.

5. The death penalty is disappearing

Out of 198 countries around the world only 21 continue to use capital punishment. And while countries that carried out executions in 2011 did so at an alarming rate, those employing capital punishment have decreased by more than a third in the last decade. With this clear downward trend, public pressure may help persuade the world's biggest executors China, Iran, Saudi Arabia, Iraq and the USA to stop.

There are countless arguments for and against the death penalty. In an imperfect world where we can never be sure we have ever got the "worst of the worst" is it ever justified to take a life?