The fish on the wall has its mouth open because it couldn’t resist the temptation to open it when the occasion appeared to justify doing so. There are few convicted defendants who likewise could resist the temptation to open their mouths and thereby assist their prosecutors with their own words. The frequency with which this happens and the value attached by prosecutors and indeed jurors to the accused’s own words has not diminished the jurisprudential disquiet at requiring a suspect to answer questions, notwithstanding the probative value that such answers may give.
This of course is because it has long been understood that an element of compulsion is capable of rendering even the most apparently cogent admission unreliable. At Runneymede in 1215 King John (under a degree of compulsion agreed to include) at paragraph 38 of Magna Carta the fundamental principle that,
“In future no official shall place a man on trial upon his own unsupported statement, without producing credible witnesses to the truth of it.”
Interestingly, although appreciating that compulsion, usually in the form of torture, was capable of rendering a confession unreliable and something that required corroboration, Magna Carta did not render torture induced confession evidence inadmissible because of the use of torture: it rendered it inadmissible only where it was unsupported and as such was unreliable. Magna Carta therefore outlawed reliance upon the product of the torture unless that product was supported by credible evidence as to its truth. English jurisprudence advanced in 1215, not by recognising that torture was inhumane and contrary to the rights of man but, by recognising that a defendant should not be convicted upon the basis of unreliable testimony produced as a result of it.