Let’s not accept the exception to the rule as a substitute for the general criminal justice rule. Particularly in cases where the stakes are as high as they are in murder cases. Especially when the penalties are either death or life imprisonment without the chance of parole.
The Dzhokhar Tsarnaev case is the exception. Very rarely do you have defense attorneys get up in the beginning of a trial to proclaim their client guilty as charged. More often, there is some question as to guilt or innocence.
Take instead the Washington D.C. case of Santae Tribble. Mr. Tribble was a 17-year-old man in 1978. That was when he was accused of murdering a taxi driver. Thanks mostly to the expert testimony of an analyst with the Federal Bureau of Investigation about DNA found on hair strands, Mr. Tribble was found guilty and received a sentence of 20 years to life in prison.
It turns out that the expert had been wrong. The hair did not belong to Mr. Tribble. In fact, it turned out that some of the hair was not even human hair. It had come from a dog.