Feelings about guilt or innocence of a defendent & ’a-ha!’

By Anna Sandiford 20/07/2011

This is part one of the answers to the competition set up by Grant Jacobs to win a copy of my recent book, Expert Witness.

Katie Brockie was the distinguished winner and her questions and my answers are:

Do you develop strong feelings about the guilt or innocence of a defendent in a trial in which you are an expert witness?

Expert witnesses, whether they are scientists or otherwise, have a duty to remain as impartial as possible. The duty of the expert is to the court, not to those instructing them. These two key points are part of the Schedule 4 (Judicature Act 1908) NZ Court Code of Conduct for Expert Witnesses, which unfortunately are not compulsory but are a standard to which the NZ courts would like experts to adhere.

NZ is not well known for a formalised structure in which forensic scientists must function although professional bodies such as the international Academy of Experts, the UK Forensic Science Society and The Australia and New Zealand Forensic Science Society have excellent Codes of Conduct and Ethics and the UK has developed very well established guidelines and rules for expert witnesses.

As a result, in theory, experts should have no demonstrable bias; scientific findings should be interpreted impartially and within a framework that minimises the risk of accidental bias, such as a Bayesian/Likelihood Ratio approach. Again, in general terms, NZ is neither consistent nor very good at sticking to this sort of structure so biases do creep in – I see them regularly.

In the absence of compulsory requirements along the lines of those in other countries, I expect that I and any consultants I use should interpret findings as impartially as is possible by adhering to relevant Codes of Conduct & Ethics and an impartial assessment of findings. This means not forming an opinion on someone’s guilt or otherwise.

Although this would appear to be a challenging situation, in reality a scientist is very rarely privy to all the details in a case and therefore should not feel suffuciently informed to form an opinion on guilt or innocence whilst the case is in the investigation and trial stages. Allowing feelings to interfer with a scientific interpretation whilst a case is in progress is potentially dangerous and should be avoided; the key is to recognise that it might be happening and do something about it (such as work on another case for a while or talk to a colleague about it. In the most difficult cases, a scientist would ideally step up and say that they were too emotionally involved and that it would therefore be inappropriate to continue).

Having the type of personality that allows you to compartmentalise your life also helps alot. Once the lab door shuts at the end of the day, a case very rarely keeps me awake at night. It might seem heartless or cold but it’s a survival tactic.


Do you ever enjoy an ’a -ha I’ve solved it!!’ moment when you are doing a forensic investigation?

This question is kind of linked to the last answer; a scientist rarely knows all there is about a given case so it would be difficult to be able to say “a-ha I’ve solved it” unless they were privy to all relevant information, not just the scientific findings.

However, a variation on “a-ha” moments do occur. The best “a-ha” moments for me (because they are instantaneous) have been in footwear cases where I have examined a crime scene mark and compared it with the sole of a specific shoe. This usually involves using a lifesize photograph of the crime scene mark and overlaying an overhead transparency sheet on which is an impression of the sole pattern of the shoe. You move the overhead transparency around to see how well (or not) it matches the mark from the crime scene. Sometimes, you slide the transparent sheet around and it all falls perfectly into place – as conclusive a match as you can get. It’s a very satisfying feeling and I have found myself saying “a-ha!” without realising it. It’s not a common occurrence and other people are usually attracted to the sound, which instantly gives you a chance to make sure you’ve got it right because they want a look too.

Unfortunately, even in cases that seem apparently straightforward, there’s usually something that doesn’t quite tie in or that doesn’t match as well as might be otherwise expected, but that’s just the nature of the job.

0 Responses to “Feelings about guilt or innocence of a defendent & ’a-ha!’”

  • Thanks!! Great answers, and I’m looking forward to reading your book.