I have appeared as an expert witness quite a few times in a past life, albeit always at magistrate / sheriff court level and in connection with food quality / contamination issues. My view is that flipping a coin would probably give a more accurate judgement. I was normally asked to appear by a food company although at times I did warn them that sometimes my evidence might not be to their advantage but I would have to give it as I saw it.
Anyhow let me give you an example of a case where I thought that there was a cut and dried ‘not guilty’ verdict coming.
The case involve a metal bolt in a sausage. By the time I got the evidence it had been mauled by a public analyst. However it was clear that the sausage had been cut along its length and the bold was more or less central and the head had been approximately flush with the plane of the cut with the shaft of the bolt at right angles to the length of the sausage. That in itself is unlikely. We put some bolts of the same size and shape through the sausage filler at the Research Association where I worked, and admittedly with a small sample size, they tended to go through into the sausage with the head leading the way and with the shaft following at an angle of about 30 degrees. The head normally went towards the outside of the sausage. This would be expected as the sausage meat would tend to push the head forward with the shaft following. I analysed the metal that the bolt was made of and found it to be cadmium plated, such bolts would not be allowed in food machinery. The bolt was a good match for bolts used in telephone exchanges at the time.
The public analyst had reported that as he pulled the bolt out of the sausage with tweezers the force require was such that it indicated that the bolt had been cooked inside the sausage rather than being pushed in afterwards. We cooked bolts in sausages, pushed bolts into sausages and screwed bolts into sausages and measures the force required to pull them out with an Instron and found no difference between the force required pull out the bolt between that which had been cooked in the sausage and that which had been pushed in and a very small,increase in the force required to remove the bolt that had been screwed into the cooked sausage.
My colleague, a meat technologist, carried out a factory inspection and found no bolts resembling those found in the sausage (though he didn’t go 30’ up to the roof to inspect the sheilded fluorescent light fitting). The metal detector consistently rejected a pack of sausages with the bolt inside one of the sausages and the factory records showed that the metal detector was functioning correctly and had been checked as required on the day the sausage had been manufactured.
In my view we had assembled irrefutable evidence that the bolt had not got into the sausage in the factory. Certainly enough to to raise reasonable doubt that it had been the result of a factory incident.
At the court case the complainant who was a telecom engineer working in an exchange gave evidence. He was a middle aged slightly below average height and slightly above average weight for his height, bespectacled and balding. Asked for his account of how the bolt had been discovered he responded “I was making supper for my disabled wife……..”. At this point I thought that simply because the alternative to it being a factory incident was, effectively, to accuse him of deliberately putting the bolt into the sausage that the magistrate would find it easier to find the company guilty, which he did. Perhaps the under threat Scottish “not proven” verdict (which was in my view the most appropriate verdict in many of the cases I was involved in) would have provided an escape route for the magistrate.
I'm intrigued as to why the company in question did not rely on the standard "due diligence" defence available in cases of "foreign object" contamination.
I'm unsure if the case was a formal prosecution as you infer the prosecution evidence seems to be reliant on testimony from the public analyst although I suppose it could be a civil matter brought by the purchaser if he sought assistance from the public analyst rather than some general food "scientific services" company they would normally be referred to.
As you say in this case it seems perverse to find against the company when they have availed themselves of all the appropriate technology to avoid such contamination and documented processes to ensure such technology was working and no doubt calibrated.
For clarity I have been present on many occasions in such food factories to witness the testing of exactly the machines you refer to that extract contaminated foods from the production lines. Often they have 2 machines, one an x-ray based machine and another is a magnatometer. They have several test items containing gradually smaller pieces of debris or metal. I forget how small the due diligence defence allows but my memory says its something like 1mm to 2mm. Something the size of a bolt would never pass through these machines unless they were defective. They are checked at a minimum daily and good quality control would see several checks daily, usually per batch produced but occcasionally random, similar to average weight checking. The QC operators would simply insert the check item onto the production line and record its automated removal. Its just good practice.
I've been witness to many of these types of complaints, usually made to the local authority where the purchase was made and sometimes referred to the originating authority where the goods were produced. Members of the public are mostly unaware that scientific analysis of dead mouse parts, cockroaches, earwigs, pieces of plastic and other foreign object debris can reveal if its been through a cooking process or not. (Thereby indicating if it was present before it was cooked and not inserted afterwards).
99% of food producers take extreme care to avoid such circumstances as the severity of successful prosecution can be fatal to their business. It's therefore very unusual for such a case to be In front of a magistrate and I would suggest that the clerk must have been poorly informed to advise a magistrates panel to subsequently reach such a finding.
That's not to say some individuals are not successful in absolutely taking the piss or may have a valid case of complaint. In this case it would seem ignoring the due diligence and then assessing the liklihood of harm that no normal person is going to not notice a metal bolt in a sausage so it's mighty convenient the person offended was disabled and therefore more vulnerable.
I've submitted evidence similarly in courts only for magistrates or judges to ignore or not give significant weight to your findings so I feel your pain at seeing perversions of justice. As a barrister once mundanely professed to me, "You win some, you lose some". Its part of the system. Interestingly did the company not appeal on "case stated"?
I know at least where I live an Environmental Health manager sits on the magistrates panel and would have laughed this one out of court.