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?

Joe Kebartas of South Boston protests the death penalty outside of the entrance to the John Joseph Moakley United States Courthouse © Getty Images

What if the death penalty wasn't only reserved for the "worst of the worst"? Or, what if innocent people were tortured to confess to a crime they didn't commit?

The death penalty is cruel, inhuman and degrading and Amnesty opposes the death penalty at all times – regardless of who is accused, the crime, guilt or innocence or method of execution. Here's are five reasons we must challenge the notion of "an eye for an eye".

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 was executed in Texas in 2004 for allegedly setting a fire that killed his three daughters. Following his execution, further evidence revealed that Willingham did not set the fire that caused their deaths. But it came too late.

2. It doesn't deter criminals

There is no credible evidence that the death penalty deters crime more effectively than a prison term. 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.

Revenge is not the answer. The answer lies in reducing violence, not causing more death.

Marie Deans, whose mother-in-law was murdered in 1972

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 brutal 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. According to UN human rights experts, executions in public serve no legitimate purpose and only increase the cruel, inhuman and degrading nature of this punishment.

“All executions violate the right to life. Those carried out publicly are a gross affront to human dignity which cannot be tolerated,” said Hassiba Hadj Sahraoui, Amnesty International’s Deputy Director for the Middle East and North Africa.

5. The death penalty is disappearing

Act now online

Stop the imminent executions in Indonesia

TAke Action

While executions spiked in 2015, they were counterbalanced by a spate of abolitions. Four countries abolished the death penalty for all crimes – the highest number to do so in the space of one year for almost a decade. These developments are a clear indication that the trend towards abolition remains strong.

Today, 102 countries – half the world – have turned their backs on the death penalty for good.Those that continue to execute are a tiny minority standing against a wave of opposition.

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?