Sunday, 7 December 2008

Thoughts on DNA retention

Nerd for Justice criticised my reasoning in this post. My reply became a little lengthy, so I’ve made it into a post.

Comparing the series of events:

Kill someone, leave DNA, get arrested later, have DNA taken, get caught due to DNA match

Previous arrest for something else, have DNA taken, found innocent of crime, subsequently kill someone, leave DNA, database is searched & DNA is matched, get caught,

NfJ sees no difference. Of course, the former is what happened, and the latter is the sequence that the European Court struck down.

My view is that I have no problem with retaining DNA samples from crime scenes. I have no problem with taking DNA from arrestees. I have no problem with testing those samples to see if they match old DNA crime-scene samples, just as I have no problem with arrestees being interviewed on the subject of anything suspicious found in their pockets, for example.

Where I have a problem is with the retention of the DNA of those found to be innocent, or not found to be guilty. This seems to be a very serious intrusion. DNA mismatches do happen - vide the Omagh bombing trial. So those on the database are at risk of having, in effect, to prove their innocence at a future date.

Such a serious step could only be justified if it were absolutely necessary. I simply cannot see how it could be. If the assumption is that we need to retain their DNA because they are likely to commit offences in the future (a logic which will be offensive to many innocent arrestees), then surely it follows that they will be arrested again in the future for one of those offences. At which point, the DNA match can be made again and they can be matched with all their offences.

In short, either you think that one arrest doesn’t imply that people are likely to offend again, in which case there is no need to keep their DNA, or you think that they are likely to offend again, in which case there will be further opportunities to match their DNA and, again, there is no need to keep it.

I would only be wrong if there were no statistical connection between offences and arrests, i.e. that we cannot assume that a serial offender will be a serial arrestee. If that connection is absent, though, we may as well just give up and save all the money spent on police budgets.


  1. If you can keep the DNA of the innocent on file then logically you should DNA test everyone at birth as they are innocent today but may go on to commit a crime { at the exact rate of the crime some 5-10% of these babies will definitely commit a serious crime at some point}

    The ruling prevents this backdoor creation of a UK population DNA database.

    O/T ish but there need to be two new laws added to the many hundreds in the Queen's speech.

    Anyone who says "If it prevents just one .." baby P/ child abduction / train crash/ burglary / divorce / double glazing salesman / terrorist etc
    needs to be subject to the new
    GROW UP! law.
    Fixed £100 penalty fine

    Ditto anyone who uses the phrase "if you have nothing to hide you have nothing to fear"

  2. Nerd for Justice9 December 2008 at 20:36

    Well... I'm going to think aloud here.

    I wouldn't say I see NO difference between the two sequences.

    The first sequence relies on certain elements of luck. First, you have to assume that your serious offender who left his DNA then goes on to reoffend. Then, having got him in custody for the later (and quite possibly unrelated) offence, you'd have to get the arrestee's DNA analysed and run against the database, while the clock counted down from the moment of arrest to the moment of release-or-charge. If you don't get the results before he's released, you have to hope he won't skedaddle.

    The second one makes the crime very much easier to investigate- get DNA from crime scene, send it to the lab, compare with database, get results back, go and arrest suspect.

    So the detection of crime is far more likely to succeed if the DNA is previously and routinely on file- EITHER following a minor crime, OR as part of a universal database- BEFORE the serious crime is committed.

    Now... EITHER following a minor crime, OR as part of a universal database... I used to be of the 'nothing to hide, nothing to fear' opinion (sorry, Bill).

    But, seeing how careless the government is with personal data, and having heard about how savvy scrotes can contaminate crime scenes (eg with a Hoover bag), I've got less comfortable with that.

    And Patently's now crystallised that feeling by writing "So those on the database are at risk of having, in effect, to prove their innocence at a future date".

    That's exactly it- there IS a downside to being on the database, and it's a risk of innocent people facing a trial with the burden of proof reversed. I hadn't thought of that as a significant risk before, but the more I find out about DNA forensics, the more weight I attach to it.

    So... OK, you've convinced me. Three cheers for the ECHR ruling.

  3. BQ - a GROW UP! law - what a wonderful idea :-D

    NfJ - wow ... I persuaded someone! Yay!

    I paused over your comment that in the "re-arrest" possibility, the practicalities of custody might mean that the offender is long gone by the time the DNA match is made. You may have a point there - although it didn't happen in the Bowman case, and in a case where a match is amde to an old arrestee's sample, that could be years or decades old so he will be even longer gone!

  4. It never ceases to amaze me that people let themselves get caught in this way.

    Genetic fingerprinting's been around since, IIRC, 1986.

    What sort of idiot is it who gets himself arrested for something trivial, when he knows he's done something serious in the past and his DNA's probably on file?

    It's lucky for the rest of us that criminals tend not to be bright.

  5. >> criminals tend not to be bright.

    Well, not the ones we catch, anyway ;-)