Why Retrials Can Offer Freedom

So, imagine that a person gets convicted but appeals, and, on appeal, his sentence is reversed on a technical point with or without proof of prejudice, and he gets a new trial. If this is indeed a technical point, then the remedy of a reversal wouldn't be worth much because the problem would be easily corrected at retrial. This is not so much the case: "The passage of time, erosion of memory, and dispersion of witnesses may render retrial difficult, even impossible. Thus, while reversal may, in theory, entitle the defendant only to retrial, in practice it may reward the accused with complete freedom from prosecution." United States v. Mechanik, 475 U.S. 66, 72 (1986) (internal quotes and brackets omitted) (quoting Engle v. Issacs, 456 U.S. 107, 127-28 (1982)) (quoted by Brecht v. Abrahamson, 507 U.S. 619, 637 (1993)).