Schneier on Security

Clive Robinson • April 4, 2009 7:49 AM

It’s funny we talk about the “science of” with regard to crime and it’s investigation as though the words lend credability to the process…

The simple fact is that the basic premise of this “lofty ideal” is “The Lockhart principle”, which simply states that,

“Wherever there is contact between two objects, there is a transfer of material between them”

Thus the usual assumption that “contact evidence” shows you where at the crime.

What is not talked about is that it also implicitly says that all investigative methods are known to be contaminated, and thus are prone to be unreliable…

In most forms of science there is the accepted “signal to noise” idea, that is the smaller the signal the more difficult it is to make a determanistic measurment (I know somebody will think Heisengburg but that is not what I’m talking about).

It must be obvious to any that actualy care to think about it, there must be a cross over point between the noise and any signal you are looking for, where you are deluding yourself if you go any further (the same as seeing meaningfull shapes in clouds or the “static” on a TV that is not tuned in).

Sadly as has been witnessed on many occasions even “real science” suffers not just from this “self delusion” but due to “vested interests” (reputation and money being just a two of a long list) it actualy encorages it…

If you accept that and then further think about the well reported methods used to coerce people (plea bargining, reducing sentance etc) you can only start to question if any conviction is safe…

The principle of law in Britain and other parts of the world (sadly not Europe in general) is “balance of probability”.

This gives rise to the idea of circumstantial evidence by people that do not understand in any way how to deal with probability (and lets face it if you read enough science papers you begin to think how true this is of science as well).

Just as a point,

In an area you frequent a woman who you think you vaguly recognise is found dead with her throat slashed.

You get picked up and told your DNA and fingerprints where found on the murder weapon.

What do you do when offered a plea bargin or being “fried in the chair”.

Now think how you would feel if you find out the weapon is a broken beer glass and that your DNA and fingerprints where found on the unbroken base of the glass…

Then when you think how a bar works when washing and storing glasses.

In a lot of bars they have a machine that you turn the glass upside down and push down between rotating brushes. You then pull it out and whilst still wet it is put on a beer cloth to dry. Because the bar staff do not want to stick their fingers in the machine the outside base of the glass rarely gets cleaned.

If it’s towards the end of the evening or a quite period after a rush the glass gets put back on the shelf . The next time the glass gets taken off the shelf to be used is dependent on how busy the bar is from then on.

If you happen to be a visitor to the bar who was only there to celibrate a persons birthday or New Years eve etc then the glass you used which has not had it’s base washed could sit on that shelf right at the back and not get used for months…

Now ask yourself if you would belive that as a jury member if presented by the defense?

It is why nearly all convictions on circumstantial evidence are effectivly unsafe but nobody likes to talk about it because it is a Pandora’s Box.

In times past most criminals where caught due to their “locality” to the crime and that they where stupid. Even now a very large number of criminals are caught because the do silly things like hide the items they have stolen in their home, post videos of themselves driving a stolen car on UTube or boast about what they have done to others…

And it is this “stupidity” in the majority of cases that realy convicts them not a DNA database, DNA evidence, fingerprints or shoe prints etc, it is realy just a “side show” to convince those who stand in judgment that “justice is being seen to be done”…

However the cost of the “side show” is high but required to counteract the likes of “CSI”, “soap operas” etc which the “ordinary person” who might sit on a jury watches.

It is why having the right “legal team” is such an advantage they can “play the jury” to gain “credability advantage”.

Sadly that is why (in the UK and US) the system is being changed by those in charge to reduce access to juries and good legal talent…