Incredible evidence.

Three kinds of forensic evidence are investigated here - video enhancement, fingerpringing and DNA fingerprinting. The latter is regarded as the ultimated forensic test -but is it really infallible? The programme surveys the possibilities of error due to laboratory mishandling of samples and investigates the likelihood of random matches. Two criminal convictions, one in which a laboratory error was made, and one in which the DNA evidence is suspect, are examined. Prof. Alec Jeffries, originator of the technique, defends its reliability and Simon Ford, a U.S. DNA expert, explains how mismatches can occur.