Reply to post: Re: DNA and ffingerprints's Wayback Machine is legit legal evidence, US appeals court judges rule

Anonymous Coward
Anonymous Coward

Re: DNA and ffingerprints

@Alan Brown,

They're both great tools for proving someone is NOT the perpetrator (ie an elimination tool)

Unfortunately when it comes to proving someone IS the perpetrator, it's a lot harder, as they've both historically relied on too few nexus points for fully accurate matching - but have then been oversold by being "totally accurate"

Absolutely. Worse still, here in the UK you are not even allowed in court to point out that DNA has this problem. Judges refuse to allow a jury to be told that a DNA match is a probabilistic thing. This has led to miscarriages of justice, case reviews, etc due to the use of too few nexus points. I know of one case where the DNA match was overturned, simply because the convicted man had the money for a more detailed analysis techniques be done. Turned out it was a close match, but not an exact match.

It also means that you can have 30 witnesses saying that you were 100 miles away from the scene of the crime, but their testimony is trumped by a DNA match. One potentially mistaken scientist's view is more significant than that of all your mates. The same goes for fingerprints, and poor quality assessment of dabs has played a role in miscarriages of justice in Scotland, taking a disgracefully long time to work out.

The use of DNA to exclude people as suspects is also doubtful. Chimerism is a recognised condition, thought to be very rare. Essentially a person can have different DNA profiles across their body, as a result of 2 sperm fertilising an egg at the same instant.

However it has played a role in court cases in the USA (a mother was found not to be the parent of her child, something that was eventually sorted out when it was discovered that she was chimeric. It was a major problem, and it took a long time to show that she hadn't been commuting social security fraud).

Anyway, a crime scene DNA profile of blood might not match a mouth swab DNA profile. The problem is that the medical world has no idea as to the true rate of chimerism, because to measure the rate you would have to do a DNA profile of every part of every body who dies. The current estimate of how common it is is based on how often it is detected in the living. Trouble is no one is looking for it in the living in a systematic way, so we actually have zero idea. We might all be chimeric for what we know.

Essentially it is extremely difficult to challenge scientific evidence in court. Fingerprints, DNA, other forensic evidence, medical assessments. Judges have ruled that it is all "independent and reliable".

The medical opinion reliance is very odd; it's the first opinion they take, not the concensus opinion. Thus if a junior doctor on a late shift after a 100 hour week writes down "this was child abuse", a defence is not allowed to challenge that no matter how senior a consultant they roll out, nor how many of them. That weird approach to complex medical matters has led to all sorts of problems.

Basically, courts and science / technology are a dangerous mix. Judges want facts from individuals, but science is rarely giving them, and scientific / medical opinion is all about peer reviewed consensus not individual views. This is why 2 rogue paediatricians were so instrumental in the jailing of innocent bereaved mothers.

Anyway, the Way Back Machine had better not ever get hacked, or conceal that if it happens. If it does then it use by prosecutors in old cases would have to be questioned, and old cases reviewed.

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