And we also have deepfakes, AI, GPS spoofing, forged cell tower records. Eye witnesses are notoriously unreliable. Ad technology changes, so opportunities to exploit it change.
Is there any doubt in your mind
Due process doesn't depend on what's in my mind or yours. That's fundamental to hoe due process works.
there are crimes where we can say with 100% certainty who the perprator is.
Who is "we"? In terms of the criminal justice system, who is "we"? Stop and actually think hard about that. And then think harder.
In the criminal justice system, there is no "we", in the sense of "the British public". The nearest to "we" is the jury of twelve ordinary people, and they occasionally get it wrong.
What you seem to be advocating is a system in which the death penalty is allowed as long as a jury convicts and then you, individually, decide that you trust that jury to have given a true verdict. That is not what fair due process looks like.
What you seem to be advocating is a two-tier sentencing system where we imprison people who probably did it and kill those who definitely did it. People who only "probably" did it should be acquitted and released, not jailed.
If the jury are not sure of the defendant's guilt, they should acquit, every time. Appeals are not granted to everyone who applies for one, there has to be grounds.
Tell me that you don't understand the core principles of criminal justice upon which this country is built without telling me...