Instant Genius - How plants solve crimes, with Prof David Gibson

Episode Date: August 26, 2022

 You can’t escape plant matter. It’s everywhere. That’s why forensic botany – the study of plants to help investigate crime – is so powerful. Professor David Gibson explores how true crime cases have been solved using plants, algae, fungi and more. Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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delivering digital precision with analogue warmth. So you can experience exceptional sound at home. Music just as the artist intended. Visit name audio.com. to learn more. From BBC, science focus, this is instant genius, a bite-sized masterclass in podcast form. I'm Daniel Bennett at the magazine's editor, and today we're taking a look at the world of forensic bodily. Study of our plants can help catch criminals. I'm joined by David Gibson, a professor of plant biology at Southern Illinois University. Davis' new book, Planting Clues, how plants solve

crimes traces the rich history of botanists being called in to use their skills to help connect suspects to a crime scene or a place of interest. Before we dive in, I think it's worth a quick warning that this is a discussion of forensics and of crime scenes. So there will be talk of death and identifying the dead in what follows. To kick things off though, here's David explaining why plants are so useful when it comes to investigations. It's a part of the bigger picture for solving crimes. And so plants' evidence can help. But they're useful because they really encompass quite a broad spectrum of sizes and scales.

You know, big pieces of plants can be important, like smuggling of wood or something. Down to pieces of leaves can be important. down to parts of plants that no one can see with the naked eye, pollen, spores, and tiny little diatoms or algae, a criminal will have no idea that they're transporting or carrying on their body or in the mud on their shoes, evidence that they just would have no idea that is going to incriminate them and link them to a crime scene. So plants are really quite useful across a whole range of spectrum. Yeah, it definitely struck me that in a lot of the cases that you talk about, and we'll get to some of those in a moment,

it sort of feels that you can't escape plant matter in one way or another. Is that true? I think it is true. Yeah, I mean, I think, you know, every time we walk out in the woods or out into our garden, we're going to get a little bit of mud on our shoes, and that mud is going to contain perhaps some plant seeds. some bits of leaves, things we can see. It's also going to contain pollen.

Just walking around, we're going to get pollen up our nose. We're going to get pollen on our eyebrows in a hairline. And those are all sorts of evidence that can be extracted from either a suspect or from a body. And so, yeah, some of these plant fragments and pieces are ubiquitous in the environment. and they're everywhere. One of the examples in the book that really struck me was the diatoms. Yes. They can even be inside you in your bones.

Is that right? Yes, that's the diatom drowning idea that when a body drowns in water, those last gasps of breath are so powerful trying to get something, some air into the lungs that the water. that the water gets through the alveoli in the lungs, the fine capillaries, into the bloodstream, and the heart is still beating.

And so it's transporting blood around the body. And so these diatoms, which are tiny, can actually pass them into the blood, and they'll end up in the major organs like liver, and they end up in the bone marrow. And so if you find, if a coroner in an autopsy, finds diatoms in the bone marrow, the only way that those items could have got there is the body was drowned.

That's different to if a body was already dead and dumped in the water. And that's an important thing to know when you find a body in water. Yeah, whether they were dumped there or sort of held there, I guess. Yeah. And so how common, so again, because the sort of the range of cases in the book is so hugely varied. How do you, how does, you know, botanists are called in as expert witnesses in a number of cases. Is it something that is taught or is it something that is actually quite young and people are kind of, you know, you give lots of examples of different experiments that have to be done once

expert witnesses are called in. How common is forensic botany these days? Well, my understanding is it's not as a common as it might be implied by the plethora of cases that I talk about. My understanding from talking to crime scene investigators is that they normally don't think about plants and they're not trained in plants. So I think in most cases, this is a sort of evidence that's maybe overlooked. Now, if something is noticed or seen or they're perhaps trying really hard to find some key evidence, they'll then have to find a botanist, basically, and to look at the evidence. Now, some people like Mark Spencer and Patricia Wiltshire, a couple of British forensic botanists

have been through their career called in to cases. And from what I understand from reading their work, you know, that they get somewhat routinely called in by when the police realize that there's a value in. and botanical evidence. So I want to go into some of the examples in the book, but I thought first it might be worth discussing the idea of the four-way linkage theory, which you explained very well in the book. Can you just explain what that is and how sort of a forensic botanist sort of fits into that idea?

Yes, well, the idea between that linkage theory is that you're trying to use evidence to link a suspect and a body to a crime scene. So if you can use evidence, botanical evidence in this case, to show that a suspect was at the crime scene or with the body, then you've got these links. And so that's simply the idea of linking bodies to suspects to crime scenes using evidence. And that's where botanical evidence can come into play. And that's, that's, that's, so in one of the examples that was used to sort of rule out a very famous person, Ted Bundy, as being in a certain location, which I've sort of found quite fascinating because it's, if you could sort of give us that example, it's such a, it's such a small detail.

It is. Yeah, that was a case where some, some, some mark and and be put on a tree that suggested that it was related to the kind of the number of the the number of the person that had been killed and it was in a location where where bundy had been active where he they knew he may have buried some bodies and so forth and so they actually asked him you know did you did you do this and he said he's apparently used to talk in the third person but he said no, Bundy wasn't there or something. But they looked at the tree, and when trees get damaged, the bark will regrow. And if it's a superficial damage, then it doesn't grow as much.

There's a deep cut. And so in this particular case, they'll be able to look at the extent of regrowth and work back was defined to work out when that damage occurred. and it turned out that Bundy really wasn't there. I think he was in Florida at the time. And so he was telling the truth in this case that he actually wasn't there. And so it was someone else, it was either unrelated or some prank. But now he got caught with some other botanical evidence that did catch him.

Yeah, tell us about that. So that was when they finally caught him, I think maybe his last crime they caught him for, you know, he had a rental vehicle. and they found soil and plant materials caught up in the undercarriage of the vehicle. And when they looked at that, they were able to match the vegetation to the where they found the body. So that linked him to the crime scene. So when I read that, I did, how do you go about doing that? How would you match vegetation in a sample like that? Because obviously to, you know, someone like myself,

they would look very similar, I imagine. How does the botanist's identity start breaking down and analyzing, you know, the two samples? Yeah, well, so I think in this case it was some leaves. And so you have to, you know, take the fragments that you might find, that caught up and the undercarriage of the car, and if the pieces of leaves, you'd taken back into the lab, you'd perhaps wash them carefully so you can look at the pieces of fragments.

And if they're not something that's obvious, or even if they are, you would make a comparison match. So botanists have herbaria that are collections of dry plant materials that are reference samples. Right. So Q Gardens has one of the largest, the most complete ones in the world. And so you can take your sample

and you can match it up against these knowns. And you might have to look at microscopic characters for leaves you'd be looking at hairs on the leaves and the size of the cells, perhaps the shape of the leaves, the lobing of the leaves, a lot of different features you'd look at. And it may take some time

to work out what, what different species you have. So you may have four or five different leaf fragments representing two or three different species. And then you'd say, okay, well, this collection of species was also present at the crime scene, but not perhaps at the place where the person was living or claimed to be. And so is it a, again, forgive my naivety,

but is it a brute force sort of task or are there very, are there significant structures that you can look for that will put you in the right, the right branch of the sort of the tree of life to understand what you're looking at? Yes, there are. And it sort of depends upon what sort of material you're looking at. If you're looking at pollen or leaf fragments or seeds, you know, there'd be different sorts of characters that you'd look at and so forth. But, you know, certain plant families or plant groups have very characteristic features of them.

I mean, you know, you probably recognize an oak leaf fairly obviously, right? And so you see that and you see that kind of lobing on the leaf, the raveness on the outside. And that would probably, right away, you could probably say, oh, I've got an oak of some sort. Then you've got to get down to what sort of oak is it? In Britain, you've maybe only got two different sorts of oak, native ones. In southern Illinois, where I am, there are 19 or so different species of oaks. And so it can get kind of tricky. And that's when you have to look into details.

And there are books and there's the Herbaria and for other sorts of plant materials like wood, for example. They've developed computer databases and machine learning techniques that can help speed up some of these things once the right characters are looked at and it's kind of coded and keyed into the system. Cool. And then I want to just jump to another example. So it's not just sort of what you step on or what lands on you. It's also what's inside you, what you've eaten. There's a fantastic example of how a scientist was able to figure out what a victim is eaten. Could you just tell us about how?

Yes. So yes, so this is a botanist called Jane Bach. Emeritus Professor in University of Colorado, and she kind of pioneered this approach where you might want to know what, it might be useful to know what someone had eaten the last meal, because that could help tell you where they've been. And so basically what they do is when you've got a body, you take some material out of the intestine or the stomach and look at it and see what plants are. And it turns out that when someone dies, the stomach valves shut. And so nothing more escapes.

So that's useful because then what's in the stomach at the time of death is you've got a kind of a timing because we know roughly how long things stay in the stomach after. You've eaten something a couple or three hours. So if you find it in the stomach, that means they probably ate it two or three hours ago. So basically what she did when she started this was, you know, take, well, she was first of all given slides. She didn't want to touch the stuff, but apparently she, but I think she developed some tolerance towards this. But anyway, you just, you take the plant fragments that you extract from this,

this material collect from the stomach, this kind of a solution slurry sort of thing, and you kind of wash it up and put it on some microscope slides or on a petri dish and look under a microscope. And the same sort of thing, you've got fragments now and you have to, identify them. So you're isolating what you believe of plant fragments. Yes, yes. And then you can, it's pretty obvious if it's a plant fragment versus a beetle leaf or

something else, you know, so you can, you can tell that fairly routinely. And for plants that we eat, we don't eat a great deal of different sorts of plants. There's about 60 or 70 or so different sorts of plants that are likely to be in, you know, a diet. And most people eat far fewer than that. So you can narrow it down fairly quickly And then it's a question of looking to see in the cases that she looked at Is it lettuce or pepper or olive or something like that

And it could be seeds, it could be leaf fragments Depending upon the sort of plant And did she? Amaran saying she to sort of gather evidence She chewed a lot of food herself Yeah, the beginning that's right There was no database And so she wanted to

kind of her reference samples to look like what it could be that she was looking at. And so she literally would take a piece of letters to it, I don't know, 32 times, you know, like your grandmother always did tell you and then spit it out and look at it. And so she did that with a variety of different things to build up a database. And eventually published a manual that had electromagnoscope images of plant materials. I don't know if the ones that she had eaten or not, but that was the idea. As changed by Jane Park. And then to go down even further, you talk about how sort of we can even identify sort of plant genes in cases.

Could you just give us an example of there how that can be used to sort of help solve a case? Yeah, the first case of that was called Maricopa case, the place in Maricopa County in Arizona. That's where Phoenix is. And this is a case where there was a rape and a murder, and they had a suspect from some other evidence. And they found in the back of his pickup truck some seed pots of a tree. And it's a fairly common tree, but there was several of these trees growing around where they found the body. that didn't help him too much because that tree grows elsewhere as well. Because he was saying, I wasn't there, you know, at least at first.

So this is a time when they were starting to use genetic evidence from humans, but they hadn't done it for plants before. So they pretty much just used the same methods that were being developed for human forensic cases and took these seeds and they extracted the genes. and they matched the genes of from those seeds to the plant that was right by the body. So it wasn't just the species, but the individual within the species that matched up. And so that put his pickup truck at the crime scene, that linkage we talked about before, based upon the genetic material.

And so now that's something that can be routinely used in other cases. And can you can you, is it just seeds you can do that with, can you do that with kind of a variety of plant matter like pollen? You talked about before you can try and. Yeah, yes, you could do it with plant fragments, leaves, pieces of wood, seeds and so forth. Pollen, I'm not so sure about that because you tend to, well, it travels and you also tend to get different species in the mix. You'd have to extract a single pollen grain. and that could be trickier. But I wouldn't be surprised if they're working out how to do that as well.

And so were there any cases in particular, there's, you know, they're plentiful in the book, but that really is either your favorite one to teach or that are really stuck with you? Well, the one we've already mentioned that I always like to tell people about this, the diatom drowning case, where they pulled a body out of the Hudson River in New York. and this is a case where they got a suspect from other evidence fairly quickly,

and of course, I wasn't there sort of thing, but they wanted to know it if she'd actually drown. It turned out what the suspect had done is that he drugged his wife or partner and threw her in the river, but she kind of woke up. He didn't give her enough drugs. So then he went in and held her down, and ultimately she died from the drown. And they use the diatoms to show that and to show that she'd been drowned. But also the diatoms were on other materials that they found, like a wallet or some other and some jewelry that matched the diatom, the species of diatoms that were in the river as well.

So that's a good case because people always are interested in the drowning aspect. If someone was listening to this and they wanted to start to understand the botanical world a little better, where would you suggest starting or how would you suggest beginning? Well, just start walking around outside and looking at plants. It would be the obvious thing to do. And in Britain there's a great history of naturalists and botanists and botanical society. and so forth that people could be still become members of and there's a lot of books that you can use wildflower guides to help identify plants but these days there's this phone apps that are

getting really good there's one called i naturalist that is is really good and you just literally take your phone and you turn on the camera and you point it at the plant and take a picture and then it uploads that picture and looks on its database and gives you suggestions as to what the name of that plant is. Once you put it on the database, then other people can look at that picture image and see if they agree or disagree with you. And so that's kind of fun to use that.

And do you, I sensed in the book, I mean, you have a sex segment where you talk about some of your past professors who might have scolded you for using the book. Absolutely. Yes, my PhD advisor in Bangor where I did my PhD, he wouldn't let us use books with pictures in, let alone a computer app, of course they didn't exist in. But he was very much old school. You had to have your little hand lens that you used and your flora is called that's a book with descriptions and keys to identify the plants. And will behold, any student that was caught using a picture. book. And was there some benefit to that? What was he trying to sort of impart?

Well, he's right, of course. But, you know, pictures, and even the Sikh the I naturalist app and stuff like that, you can get it wrong because a lot of, a lot of different species are, the difference between some species is incredibly difficult and you need to do

in great depth to work out one species, versus another. I mean, you know, you can tell a rose, but how many different sort of roses are there? Look at all the cultivars that you can buy and telling them apart. So it takes a great deal of knowledge to correctly identify and be sure that you really know the name of something. And that can be really important in forensic cases to get the name right. So, yeah, a botanist would not rely on a phone app or a picture book. So, yeah, so you can get. down to the general group of plants fairly readily and fairly accurately with these

other these apps and picture books and so forth but when you want to know exactly what sort of roses is for example then we use a flora is the name of the sort of book we use and that'll have a key a dichotomous key is it got this structure or that structure or are the leaves this length or that length or certain structures this size or that size and you get down to a name. And then you have to look at a description that's going to be like a paragraph long. And you're very detailed information about a whole range of structures. The flowers, the seeds, the height of the plant, the leaves, and sometimes almost microscopic characters that you're at the very least need to handle in is to work out at that level of

detail. So just lastly, how old is forensic botany as a discipline. I'd just say that it's not a totally new subject. And I do talk about this with Edmund Lockard, who was the French police investigator back in the 1920s, who was really the first person to start using plants. And he talked about le poissosers organic. Sorry about my French, but his organic particles. And he was using them to help solve crimes back in the 20s. And he had a laboratory in Lyon in France, which is the first sort of forensic lab, maybe even in the world that he developed. And just an example of one case where they found a body on the countryside somewhere,

and the local gendarmes had like trampled all around and destroyed, you know, and everything. But they brought in some vagrants that might be suspects. and he noticed on one of them a seed up on the jacket, caught up on the jacket of one of these suspects. And he knew or he went back and found out that we identified that seed. First he thought it was a common dandelion. That was his first thought. But then he looked at it in more detail, looked at these detailed structures and realized it was

quite a rare plant that was related to dandelions and went back and found there it was growing right next to where the body was found. So that single seed provided the link from this suspect to the location where the body was found. And so I thought that that's a really fascinating case in a time when didn't have the high-powered microscopes that we have today or DNA evidence, just literally working out what that seed was, what plant species happened to be, helped soul to crime. That was Professor David Gibson, though,

talking about one of the earliest recorded cases of a detective using botany to inform their investigation. If you'd like to find out more about the pursuit of forensic botany, do check out David's book, Planting Clues, How Plants, Self Punt. It's on sale now and published by Oxford University Press. Thank you for listening. The Instant Genius podcast is brought to you by the team behind BBC. Science Focus magazine, which you can find on sale now in supermarkets and newsagents as well

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