Investigating Forensic Science

17 June 2007

Interview with

Dr Trevor Emmett, Anglia Ruskin University

Chris - Thanks for coming in. Tell us what you actually do, how do you use science to solve crimes?

Trevor - Forensic science, strictly is the use of scientific techniques to solve crime, that's the formal definition of forensic science. So basically, it's any scientific information or technique that we can use for that purpose. The sort of thing we teach at Anglia Ruskin is primarily concerned with analytical science, we're analysing small amounts of evidence collected from the crime scene; DNA of course, blood, fibres, glass, residue from gunshots... But any sort of scientific technique at all really!

Chris - Hasn't Anglia set up a system where you actually stage crimes, then people come in and you take them through the various things you investigate and look for.

Trevor - Well the question is "what makes forensic science different from other sciences?" And clearly, it's a matter of context. It's not about what you're doing; using microscopes or chemical analyses, it's about collecting evidence and using that evidence in a court of law. The evidence has to be collected properly. We have to make sure that all the relevant evidence is collected. We have to make sure that evidence is stored properly, accounted for properly and then analysed properly at the end.

To do that most effectively in a teaching environment we can only really simulate a crime scene and send the students in to do what they have to do. It's not just collecting evidence; it's about securing the crime scene, controlling access, and all aspects of quality management of the evidence. If any of these steps are compromised then you can have the best scientific evidence in the world but it will be no good in a court of law, and that isn't good forensic science.

Chris - You've been working on authenticating ancient documents as well, how do you do that?

Trevor - Again, it's purely analytical science.

Chris - What are the give-aways? What are you looking for that says "this is a genuine old document" versus something I made to look old?

Trevor - It's very hard to prove a negative, of course. So what we look for is positive evidence that the document isn't what it purports to be. Some of the work I've been doing with the Fitzwilliam museum [Cambridge] on ancient Egyptian papyrus' If we found on those paintings some pigments or dyes which were only invented in the 19th century then straight away the provenance of that document is called into question.

Chris - How do you know they were only made in the 19th century? What's the chemical hallmark that says "I'm more recent than this ancient Egyptian one"?

Trevor - It's relatively straightforward for ancient Egyptian works. Ancient Egyptian pigments are nearly all geological in character, they represent coloured ores and minerals from the surface of the earth. There are some organic ones, we've all heard of 'imperial purple' which is made from sea shells, and there are one or two others. But in the main what organic colours or dyes were available to ancient Egyptians were very limited. In the 19th century with the development of the chemical industry all sorts of azo-dyes and amino-dyes were developed and a very wide range of colours were developed. SO if you find those materials, those compounds didn't exist at all until they were first made in the 19th century.

Chris - Have you flushed out any fakes?

Trevor - Not from the ancient Egyptian material, I have on one or two other things I've looked at.

Chris - What sorts of things have people tried to fake?

Trevor - They try and fake everything! I did some work on some castings, some statues, which were purportedly 2000 years old, and discovered that they contained an alloy which probably meant they were made in the 19th century. Very straightforward.

Chris - How did you know that? What was the alloy, was it something that people 2000 years ago wouldn't have been able to make?

Trevor - They wouldn't have been able to make it, no, not at all.

Chris - So how do you do this? Do you drill in to it and take samples out? Because if it turned out to be genuine I wouldn't be happy to have you drilling into my beautiful statue that I paid thousands of pounds for.

Trevor - I would never be allowed to drill into anything. I remember in one of my first discussions with a museum, we had a long discussion about what they wanted me to do. I thought asking for ten grams of material would be a very reasonable amount and I could almost hear the conservators on the other end of the phone fainting. Then they said they could send me some drillings and I was expecting to see one of those curly things that come out of your "Black and Decker" when you're drilling some wood. I got about three specks of dust! When I was working in geology, I used to think that half a gram of material was a bit dodgy for analytical work. Now if I get a milligram I think I'm doing pretty well. You get very very small amounts.

Chris - So how do you actually analyse it? Was it a case with the metal of melting it down and doing some chemistry on it. What's the way in which you actually flush out the chemical fingerprint?

Trevor - In that particular case, I took about a milligram of material. A milligram is about a quarter of a grain of sugar, a very small amount of material. I had to develop techniques for handling such a small amount of material, it's very easy to lose it. Then basically we dissolved it in acid and analysed it in the way would analyse any other solution, and the results were conclusive.

Chris - I heard a suggested technique was to fire x-ray beams at things like the statues you mentioned and the scatter pattern is indicative of what's inside, so you don't have to harm them. And because, as you've said, people are using different forms of metals these days compared with historically, this can sometimes be a give-away.

Trevor - Oh Yes. Many years ago I had a colleague who was very interested in looking at Elizabethan methods of lead smelting. We discovered that some of the artefacts that he had actually bought (and that's always a dead give-away if you buy anything) actually contained stainless steel, which is another thing which didn't exist before the 19th century. If you have a statue that has been cast in bronze, the technique will vary with time and location in the world, and you can x-ray it just like you would x-ray a human body for a broken bone. Another thing that happens when you irradiate material with x-rays is that the atoms in the material will radiate their own, characteristic x-rays. That's a technique called x-ray fluorescence, another very sensitive way of determining the composition of the material. The great advantage of x-ray fluorescence is that it's entirely non-destructive, you don't have to take samples of the material.

Chris - I heard that you can even get fingerprints from previously un-fingerprintable things using that technique. If people touch things, they can leave behind traces of sweat which has traces of metal ions in the sweat. If you zap that with highly focused beams of x-rays, you can literally see the fingerprint flashing up again, even on things like skin, which previously wouldn't have shown the print.

Trevor - I've not actually heard of that, it sounds a bit implausible, but then these things often do. I've certainly seen published techniques where people have looked at documents that have been handled. There are no apparent fingerprints but they use something called confocal fluorescence microscopy to be able to see under the surface of the document and actually see the ghostly imprint of a fingerprint on a document that's not actually on a surface. The lipids from the fingerprint, the fatty material and the proteinaceous material, have soaked into the document. This very powerful technique, used a lot in cellular biology, is able to reveal the fingerprint under the surface of the document.

Chris - Finally, talking about things leaching into other things, what about when people try to dispose of bodies in environments like peat bogs, where bodies are very rapidly dissipated. Can you tell from samples of peat if there was a body there?

Trevor - There are several ways this has been attempted, but it's never been particularly successful. You can look for the decomposition products of the human body by organic analysis, but a new technique being developed by colleagues in Northern Ireland is to look for stable isotopes. Stable isotopes of carbon, nitrogen, oxygen in the ground water, and to try and look for bodies by using the natural water system in rivers and swamps and suchlike to try to look for the body itself.

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