Dr. Jan Svartvik's linguistic analysis of Evans' forged confession statements was one of the earliest cases of applied forensic linguistics, which is a fascinating field of study.
You can read more about it here: https://www.thetext.co.uk/Evans%20Statements%20Part%201.pdf
Basically, Evans was more or less illiterate and allegedly low IQ, and Svartik compared the first of his two statements to the latter two, and found subtle but suspicious differences and was able to conclusively determine that they were forged.
Off topic, but I think a more compelling discussion would be whether we should allow the death penalty, even if we could somehow be 100% certain the convicted actually committed the crime.