"Cynic" wrote in message
news:npbo241gf61cru00cbtd73oti6rbquu27b@4ax.com...
> On Thu, 15 May 2008 08:31:51 +0100, Les Invalides
> wrote:
>
>>Yes, and of course it depends what it matches. If it fully matches a
>>semen sample found on a murdered 5-year-old's dress, that's one thing.
>>If it partially matches a saliva sample found on a cigarette end near
>>the scene of a burglary, that's quite different.
>
> Don't be so certain that a match of a semen sample on a dress
> constitutes good proof of itself.
>
> There has been at least one case that I know of when unbeknown to the
> investigators, the evidential sample did not contain any viable DNA at
> all. It was sent away for DNA analysis along with a sample from all
> the people who had known contact with the victim. A miniscule amount
> of contamination from a suspect's DNA sample to the evidential semen
> sample occured, which after LCN amplification ended up giving a
> completely false match between the semen DNA and the suspect's DNA.
>
> Also, it is by no means impossible for a criminal to plan ahead by
> planting semen from a used condom at the crime scene.
Also, one of the things the DNA brigade (nothing to hide, nothing to fear)
tend to keep quiet about (although it's always been accepted with
fingerprints) is the discovery of a sample, tells you nothing about *when*
it may have been left there. Given the ability to "recover" DNA from
degraded samples appears to be taken as given by the courts, there's every
chance that the discovery of a month old cigarette butt might lead to
someone who has no alibi for the time of a crime being fingered, as they
"must have been there".
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