Intellectually, I can see how the death penalty might be appropriately applied, but the standard of evidence would be astonishing high. Like, as in several police officers physically witnessed the defendant killing in cold blood, the whole thing was caught on video, there was overwhelming physical evidence proving the defendant did it, and the entire process was transparent and open to public scrutiny.
I am reminded of a story line in the "Astro City" comics where a lawyer got a defendant off on a murder charge when that standard of evidence was, for all intents and purposes, met. He argued that with so many shape changers, mind controllers, illusion generators, and mimics running around, eye witness accounts and physical evidence were no longer sufficient to prove guilt. Of course, then the Blue Knight just gunned the asshole down and solved the whole issue.