One of the criticisms of Mr. Skinner's trial attorney, Harold Comer (who ironically prosecuted Mr. Skinner for assault and theft) was that he never had DNA testing performed on biological material collected at the scene but never tested by the state. As Mark Bennett points out, it was probably because Mr. Comer was afraid of what the tests might reveal. However, by not having the material tested it becomes a flag you can wave at the jury.
"Why didn't the prosecutor test the material? If he had we would know for certain who committed this crime. Was it because he was afraid it would show someone else did it? Was it because he was lazy? If the existence of this untested material makes you think twice about whether Mr. Skinner committed this crime, that's called reasonable doubt -- and that means that Mr. Skinner is not guilty."
Is that what Mr. Comer did? No, it's not. He probably just assumed it would make things worse for Mr. Skinner (how it would make things worse, I'm not certain). My point is, though, that there are sound reasons for not testing, or retesting, evidence in certain cases.
In a DWI case, for instance, if a blood draw was conducted and the results of the blood test show your client had an alcohol concentration of over .08, do you really want to test the other sample? If you do and you don't put your expert on the stand to testify as to the result, the prosecutor will know why -- and, so will the jury. In most cases you're better off attacking the lab procedures, the chain of custody or the actual physical draw itself.
If the drunk driving case is based on a breath test I always ask the state's expert about the Toxitrap -- a device made by the manufacturer of the Intoxilyzer that can preserve a breath sample for retesting. The last thing I want is for the state to start using the Toxitrap. I don't want the breath sample preserved. I don't want to retest it on a gas chromatograph. I want to use the fact that the State of Texas won't spend $2 to preserve evidence in a criminal case. I want the jury to feel that it isn't fair that the state's breath test machine destroys the only evidence.
But back to Mr. Skinner for a minute, why is the state opposed to testing the biological material pursuant to Chapter 64 of the Texas Code of Criminal Procedure? The duty of a prosecutor is to see that justice is done -- when a man's life is at stake, shouldn't we be certain we're killing the right person?