I could be wrong but I highly doubt the study is actually capable of measuring literally death penalty vs life in prison as two punishments and whether the life in prison option leads to much more corruption than the death option–both are probably big deterrents if literally instituted as such.

It could also be argued that the death of certain individuals could potentially cause social unrest, dissent, or some type of martyrdom in a negative socialist direction, vs. life in prison ensuring that does not happen. Therefore possibly being the more reasonable stance.

I don’t consider this an overly important point personally nor do I give a shit about some corrupt billionaire getting got.