I read a Science Fiction book, where they had perfected cryogenics (long term deep-freeze-sleep). Instead of execution, convicted murderers were cryogenically stored for 200 years.
If evidence showed up which cleared them, they'd be warmed up & awakened. If, after 200 years, a review concluded they were definately guilty, they were "terminated" (without waking up).
When we have such a system, I will reconsider my opinion of the death penalty. Until then, while there is any possibility thae an innocent person might one day be executed, I cannot support it.