A 2007 analysis on victims’ families found that only 2.5% stated that execution of the offender gave them true closure. Groups like Murder Victims’ Families for Human Rights campaign against the use of the death penalty.
There will always be a margin of error. Even if this margin were only 0.001%, there will still be someone killed who should not have been.
The Hippocratic Oath bars doctors from administering the lethal injection, and so it ends up being done by prison employees. Of around 500 injections carried out in the US since 1982, around 20 cases have gone wrong.
This can be torture; when an incorrect dosage is given, inmates may awaken during their execution, leaving them completely aware of what’s going on – they are paralyzed and suffocating.