I called an ambulance to my home because my partner had fallen backwards and banged her head. She was not coherent at the time so the police were called. She was taken to hospital and I was arrested. After being fingerprinted and having my DNA taken, I was then asked what had happened, I kept trying to tell them all the way through the episode but they were not interested until I had been processed. after giving an account of what had actually happened I was released without charge because there was no evidence of an assault. That’s because there never had be an assault!

Now they have my DNA and fingerprints for no good reason, I feel like I have been violated - just to give a young recruit some experience, I not sure if I should make a complaint to somebody - I was put in a police van and handcuffed with my hands through the seat belt (if there had been an accident my life would have been at risk). I was then put in a police cell for two hours and after somebody finally wanted to listen to me, was released without charge! Not only was this a waste of police time and money but now I am worried where my data mite end up! - Justin Pursell

The way you match dna is using a “dna fingerprint” not using the entire sequence. With this method you have a chance of having the same dna fingerprint as someone else. The government put this chance at one in a billion. An independant audit put it at around one in a hundred.

If we assume the government estimate is right and then look at the mathematics there is still a real problem. If it is one hundred to one then there is a worse problem.

One in a billion is alright if you are doing a one to one match. If you have a large database then you are looking at large numbers of possible matches. With one in a billion probabilities on a database the size they are proposing the mathematics (combinatorics) says there will be thousands of duplicates. This means the odds are that there will be several innocent people (hundreds or thousands rather than tens) appearing to be matches to crime scene dna.

This is without even taking into consideration the fact that DNA is persistent and portable. Mathematically a database is indefensible unless we are prepared to send innocent people to prison.

I will be doing a series of articles on this subject on my blog over the next few months. I will include some of the reasoning behind the maths.