It seems an individual who had his DNA entered into the database, then went all the way to the Court of Human Rights at Strasbourg to have it removed (on the grounds that he was acquitted of the charge that lead to his DNA being sampled in the first place, not to mention the fact that he was only 11) has now been convicted of several other offences including possession of drugs.
Not surprisingly the police are claiming that this supports the current position that anyone arrested should have their DNA sampled and stored in the database, but equally unsurprisingly this exposes a lack of analytic ability. The facts of this case mainly, and quite clearly, show that the detection of this individual's further crimes or alleged crimes did not depend on having his DNA on the database at all.
The police presumption is clearly that anyone who commits one crime will commit more. Actually there is considerable statistical evidence to support this, however this isn't the basis on which DNA samples are taken (in England at least).
If it was the case that DNA samples were taken from those convicted then there would be few to oppose this, however it isn't even the case that samples are taken from those charged, they are taken from anyone who is even arrested! Therefore the actual police presumption is that anyone arrested will be a criminal, if not for the alleged crime that lead to the arrest, but for some future crime and therefore it is only sensible to take their DNA in order to detect future crimes.
What clearer example of guilt until proven innocence could there be?!
Of course in some cases the police will be right, but we do not have, and can never have, a perfect justice system. Our constitution is based on the presumption of innocence and the recognition that it is better to let the guilty go free than to convict the innocent. The DNA policy must reflect this.