I don’t know the answer to that nailit.
Maybe you would have to prove that the person was fully aware of what they were doing, but although forensics have come a long way, psychiatry is still basically an opinion, so we’re back to square 1.
The OP was If A Referendum………. and if that were to happen now, I honestly don’t know how (or if) I would vote, I just think that citing old miscarriages of justice such as Timothy Evans doesn’t work any more, because we didn’t have the science or technology back then.
I’ve always had a fascination for the Carl Bridgewater case, and if we’d have had the death penalty in 1979 when they were convicted, the 3 (still living) men wouldn’t have walked free 18 years later, but with todays forensics, would they have been convicted in the first place?