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HI, Iím Dan Krane. Iím a Professor of Biological Sciences at Wright State University in Dayton,
Ohio. And Iíd like to take advantage of the next 50 minutes or so to talk with you about
how it is that DNA evidence can be used in courts; both in the United States and around
the world. The PowerPoint slides that Iíll be using as part of this presentation will
all be available at www.bioforensics.com, and youíll also be able to find a number
of other additional materials there that might help you get a deeper understanding of the
things that Iíll be talking with you about in the next few minutes.
But with that said, letís get right to work and start talking about exactly how it is
that DNA is making its way into courts in the United States. So letís talk about DNA
technology in US Courts. First and foremost, we probably wouldnít be here talking about
this at all today if not for the fact that criminal prosecutions for about the last 20
years now have been increasingly relying upon the use of forensic DNA evidence to secure
convictions. And the reasons for that are pretty straightforward, letís just go through
the most obvious ones right out of the gate here.
First and foremost, DNA testing is providing forensic scientists with absolutely unprecedented
sensitivity, and at the same time that itís sensitive in the sense that we can generate
DNA profile information from unimaginably small quantities of starting material, itís
also possible for these small amounts of starting material to generate very powerful, very probative
evidence samples that prosecutors again are relying upon more and more. And more than
just prosecutors, jurors are coming to expect prosecutors increasingly to provide DNA evidence
to support their conclusions.
So DNA tests have the advantage of being extremely sensitive and very distinguishing between
individuals, but in addition to that, something thatís making the use of DNA tests even more
common these days is the fact that there are increasingly large databases available that
Can be used to help with the generation of investigative leads. Iím talking about the
situation whereby there is a crime committed with some evidence thatís left behind at
the crime scene, but where there is no good suspect that the police have been able to
identify. In such a circumstance itís possible to take that evidence from a crime scene,
generate a DNA profile from it, and then compare that DNA profile to the DNA profiles that
are on record for, at the present time, tens of millions of people who for the most part
have been convicted of criminal offenses, but now increasingly are including individuals
who have simply been arrested.
So again, the idea here is that this is an opportunity to generate an investigative lead
where once we had no suspect, if we find that an individual in a convicted offender database
matches an evidence sample from a crime scene that may well provide a critical lead for
law enforcement in investigating a crime. And in addition to that, itís fair to say
that for the entire history of DNA profiling the process has become not just more sensitive
and more sensitive; itís also becoming much quicker and much less expensive to generate
DNA test results. In the very earliest days of DNA profiling back in the early 1990ís
and late 1980ís it would often take months to generate a DNA profile. Today a DNA profile
can be generated in as little as a few hours. And thereís a race underway right now for
individuals to develop better and faster technology that conceivably might generate DNA profiles
in as little as a half an hour in the next few years.
So again, DNA tests are fast becoming both cheaper and faster, and even more portable;
to the point where it may be possible for a police officer at the scene of a crime to
generate a DNA profile at the crime scene itself. So again, DNA evidence comes up all
the time in courts in the United States, if for no other reason than the fact that the
prosecution has found it to be such a very powerful tool in securing convictions. And
increasingly, jurors are expecting that prosecutors will present them with DNA evidence in a wide
range of cases; not just violent crimes but even breaking and entry and extortion types
of cases now are often associated with DNA test results.
But thatís not the only reason we see DNA evidence in court. Letís look to the next
slide here and talk a little bit about the places that you might be able to get DNA evidence
from; that will give us some ideas about other opportunities to use DNA evidence. What we
have here on this slide is simply a graphic thatís showing a number of different ways
that DNA could be obtained from different evidence samples. These are common household
items for the most part and you might be surprised to hear that itís possible to generate a
DNA profile off of each of them, potentially a very useful DNA profile.
Letís look at the comb in the upper left hand corner to get things started. You can
probably just barely see it on your screen, but the arrow might help you now to see that
thereís a little white spec there. Thereís a technical word for a spec like that, thatís
called dandruff. Itís not a particularly revolutionary principle in forensic science,
but that small spec of dandruff is actually a number of skin cells that have come, most
likely from an individualís scalp. And as weíll see in just a few more slides, a few
of those cells should be sufficient to generate a DNA profile, and here that would constitute
an abundant amount of material to generate a good, solid DNA profile.
And in addition to that one larger piece of dandruff, you see that the arrows here are
drawing your attention to a few other spots that also have small specs of dandruff. Again,
any one of those could well be a suitable source of DNA for the purposes of generating
a DNA profile. But the elephant in the room on this particular slide isnít that comb
or the toothbrush or the dental floss, again, all fairly good and obvious sources of DNA,
for instance for generating a reference profile for a missing person. But the elephant in
the room is this knife, and letís talk about that for a little bit.
If we look carefully at the knife in the upper right hand corner of the screen youíll see
that thereís obviously some blood stains on it. And hereís the funny thing, when a
forensic scientists, particularly a DNA profiling expert looks at a knife like this, the focus
of their attention isnít the bloodstains on the knife, and I think that actually ends
up being for fairly obvious reasons. We often know precisely who the blood came from, thereís
usually a victim that is a very credible likely source for those bloodstains. And instead,
what weíre interested in is whatís going on at the other part of the knife where the
arrow is point to here; that handle. DNA tests are sufficiently sensitive and sufficiently
discriminating that it should be possible and it happens all the time, for a swab to
be taken of that handle and that in turn to give us some insights in terms of who it is
that might have been handling that weapon.
And again, in a prosecution, thatís usually the critical question ñ who the victim is
is often something that both the prosecution and the defense can agree to. Who it is that
was wielding the weapon, now thereís often where the controversy is, and DNA test results
can provide us with some insights in terms of who it is that might have been the person
that last handled or most handled that part of the knife.
But it doesnít end just with the prosecutions use of DNA test results. We need to bear in
mind that DNA testing is also commonly invoked these days by the defense bar. This slide
is showing you a picture of a fairly famous defendant from the early 2000ís, as well
as his lawyer. Iíll let you guess which is which. One of these individuals is a prominent
US athlete and the other is an attorney. If youíre still wondering who they are, the
tall individual is Kobe Bryant and the less tall individual standing in front of him is
his attorney Pamela MacKey. Kobe Bryant was accused with *** back in 2003, and ended
up relying heavily upon DNA test results to result in those charges being dismissed.
He and the rest of the defense team had an alternative theory about the case and the
criminal defense at the time took the somewhat unusual but increasingly common step of generating
DNA profiles from what the prosecution was suggesting would be important evidence samples.
In this particular case they took underwear from the woman who claimed that she had been
*** and the defense argument was that she hadnít been *** but rather that she and
Kobe Bryant had engaged in consensual sex. And what shored up that particular argument
was that her underwear, the victimsí underwear, in addition to having Kobe Bryantís DNA,
which again is consistent with consensual sex or ***, also had *** stains and associated
DNA profiles from other individuals. And that played into the defenses argument that this
individual had in fact had engaged in consensual sex, and it ultimately won the day for the
defense.
And why is it that that was useful for the defense? Well, ultimately itís because of
the very same things that make DNA tests so appealing to prosecutors. DNA tests, here
again, had unprecedented sensitivity where they were able to determine very helpful information
from very small amounts of starting material, and they did it in a very discriminating fashion.
So while it works for the prosecution, those same advantages can also work for the defense.
And in this particular case again, it provided some support for, in this case alternative
theories regarding the case.
And just as DNA databases can provide prosecutors with suspects for a particular case of a particular
crime, DNA tests can also be used by the defense bar searching those same databases to generate
alternative suspects that at the very least sometimes raise important questions about
reasonable doubt for a particular crime. So, what makes DNA testing so useful for the defense?
I think the short answer is pretty much the very same things that cause prosecutors to
think the DNA tests are such a valuable tool for their work.
And it doesnít end there. The topic of what I want to be talking about with you right
now is not just how it is the prosecutors and defense attorneys use DNA in court, but
rather how courts in general have come to rely upon DNA test results. And it doesnít
end just with whatís going on in court, sometimes we have to talk about how DNA can play a role
outside of court, or after a conviction has been secured. And this next slide gets us
to talking about the important work of groups like The Innocence Project, because DNA tests
have increasingly played a role in post-conviction relief. Actually, just a few days ago, in
September of 2012, The Innocence Project was proud to announce that they had accomplished
the 300th exoneration of an individual who had been wrongfully convicted.
Theyíve used DNA test results to show that this individual here could not have been involved
with the *** of his step-cousin, and thereís an interesting back story to this case as
it seems is often the case with the exonerations that The Innocence Project has accomplished.
In this particular case this individual was convicted back in 1994, and has served almost
20 years in jail for a crime that again ultimately itís been proven he had not committed. Again
the crime here being a *** and a *** of a step-cousin. Sadly he had spent almost 20
years in jail, and perhaps even more sadly much of the time that he spent in prison was
actually on death row. And this individual is one of 18 now who have been exonerated
who have spent time on death row but have been found to be as innocent as a result of
DNA test results.
These post-conviction DNA tests have been extremely important. Theyíve been telling
us a lot about ways that the criminal justice system can fail, and sometimes forensic science
itself can fail. I think itís important to bear in mind when weíre talking about these
types of post-conviction appeals is that weíre not getting a truly random sample from the
cases that The Innocence Project and other like organizations are actually looking at.
There are three criteria that have to be met before The Innocence Project will actually
go through the trouble of generating DNA test results for a convicted inmate.
First the individual has to have maintained their innocence throughout the process. There
canít have ever been a recanted confession or anything of that nature. Before The Innocence
Project will get involved it has to be clear that this individual has been adamant about
their innocence from their very first contact to the very end of their interactions with
the criminal justice system. And then in addition to insisting upon their innocence throughout
the process, itís also necessary that DNA test results might actually provide some useful
insights into the case.
In Kobe Bryantís case for instance, which I alluded to just a few minutes ago, the issue
there was was this consensual sex as opposed to ***. DNA test results rarely can give
us insights in terms of which of those two possibilities is most likely because DNA isnít
telling us anything about the timeframe or the circumstances under which the DMA came
to be with the evidence sample. So, three criteria about that The Innocence Project
is looking at ñ one is the individual has to have asserted their innocence throughout;
another is DNA test results must actually help with deciding a critical issue for the
trial. And third and it almost goes without saying but still needs to be said, itís necessary
that there actually still be material left for DNA tests to be performed upon.
In the case of this 300th exoneration, the convict in that case, the exoneree I suppose
we should call him now, is fortunate that samples were still retained 10 to 20 years
after the crime had occurred and after the trial had occurred. Thatís true for a very
small fraction of cases that go back to the 80ís and 90ís. And again, you canít do
DNA tests if there are no DNA materials left behind for tests to be performed upon. And
so again, the thing here is that these DNA exonerations from The Innocence Project are
looking at a fairly skewed sample. Theyíre only looking at those that meet those three
very specific criteria. And even still, theyíre telling us some very important things about
our criminal justice system.
For the purpose at hand today, again, I think itís clear that DNA test results are playing
an important role literally at every stage in the process of the criminal justice system;
from the point of bringing of charges to the presentation of a defense, all the way through
in some instances to post-conviction relief. But as Iíve said, these exonerations that
have been accomplished by The Innocence Project have brought to our attention a number of
things that need extra attention within the criminal justice system. This next slide shows
some of the things that weíve found to have been an issue associated with these different
exonerations.
Let me start at the beginning here by telling you that the numbers here add up to more than
100% because what weíre looking at is actually a set of multiple instances of problems with
some of these particular cases. Hereís whatís going on, let me take you by the hand and
explain whatís happening here. In a total of the first 86 exonerations by DNA testing
results, two individuals, Saks and Koehler, went through and carefully analyzed the cases
to find out how it is that an individual had been wrongfully convicted in the first place.
And they found that in 71% of those 86 first DNA exonerations, in 71% there were faulty
eyewitness identifications.
People for years have been talking about eyewitness identification not being particularly reliable,
and it turns out that these types of exonerations really illustrate that itís very commonly
the case that an eyewitness has a faulty, or in some cases, a flat out wrong recollection
of what had transpired with a particular crime. I think itís interesting to look at the next
bar though. In 63% of the cases, again, sometimes we have wrongful convictions based on two
or three or even four different problems, but in 63% of the cases the errors ultimately
were associated with problems with forensic science tests themselves.
Now again, remember the restrictions or the criteria that need to be met before The Innocence
Project would do DNA testing on a post-conviction relief case, there actually has to have been
DNA test results that could help with the case. In each of these 86 the problem wasnít
with DNA testing, DNA tests hadnít been performed in the original trials, rather weíre talking
here about problems with other kinds of forensic science; things like hair and fiber analysis,
handwriting analysis, foot print or boot print analyses, things of that nature.
Again, in over half of these 86 exonerations, individuals were wrongfully convicted based
at least in part upon faulty forensic science test results barring DNA testing. And then
the list goes on, you can see that in almost half the cases there were clear instances
of police misconduct, sometimes we found instances of prosecutorial misconduct. Sometimes forensic
scientists, while they actually performed the tests correctly and arrived at reasonable
results, misrepresented them when it came time to testifying about them. And again,
the list goes on and on, including things such as insufficient council from a defense
attorney, false testimony from some other individuals other than those associated with
the criminal justice system. And, for those who havenít been involved with the criminal
justice system, a surprisingly 17% of these 86 DNA exonerations did involve a false confession
at one point or another in the whole process.
So again, if youíd like to read more about this, this paper by Saks and Koehler was published
in the Journal of Science in 2005. And itís again based on these 86 first DNA exonerations.
But letís move on. DNA tests can be very helpful tools for the prosecution, for the
defense. It can also be helpful in post-conviction relief. I think the question now is what sort
of things might be a reasonable source of material for generating a DNA profile. And
the short answer to that particular question is pretty much anything; certainly anything
that comes in contact with an individual has a pretty good opportunity of giving us the
material that we would need for generating a DNA profile.
So that includes materials such as blood, fairly obviously, like the bloody knife weíd
seen just a few moments ago. But also things like saliva. The very first case that I was
involved with that involved DNA evidence was back in 1991 and actually involved linking
a defendant to a crime on the basis of whose saliva was on a cigarette butt that was found
at the crime scene. *** is very commonly a source of DNA evidence found associated
with *** investigations. Bodily tissues, skin, liver, brain are obviously very good
sources of material.
And the bottom line, once again, is pretty much anything that comes in contact with an
individual has some pretty good potential for having DNA associated with it that could
be useful for the purposes of DNA testing. So, letís get down to the nitty gritty here
and talk about just what it is thatís needed to generate a DNA profile. Hereís the thing
ñ our bodies are made of trillions of cells. Thatís right, trillions with a T. A big buy
like me probably has somewhere in the ballpark of two to three trillion cells. Almost every
one of those cells, and there are some interesting exceptions, but virtually every one of my
cells and your cells contains within it a perfect copy of our DNA. Thatís our genetic
blueprint, itís what it is that our cells are using to make the proteins and do the
things that cells need to do to make us healthy, functioning individuals.
So every one of those cells has a DNA profile within it, a complete set of our DNA, and
there are trillions of those cells. We shed those cells all the time hardly without thinking
about them. So if I touch the podium in front of me right now, Iíll leave behind a fingerprint.
And with that fingerprint is typically in the ballpark about 100 cells. Hereís the
thing ñ I didnít notice that I left behind 100 cells when I touched the podium. I have
trillions of them, 100 is an insignificant number compared to those trillions. And hereís
the other thing ñ pretty much every one of those 100 cells that Iíll leave behind with
a fingerprint will have within it a complete perfect copy of my DNA, including the parts
of the DNA that get looked at to generate a DNA profile.
So simply having touched something is enough to leave behind, at least theoretically, what
it is we need to generate a DNA profile. Iím going to bore you perhaps for a few seconds
here by talking with you about some pretty intense numbers, but check this out. The human
genome, the sum total of the DNA inside of each of my cells weighs in the ballpark of
six to seven picograms, a tiny amount of material. In just a minute Iíll take you by the hand
and talk with you about just how tiny that is. But each cell has about six to seven picograms
associated with it. The kits that are used by crime laboratories to generate DNA profiles
recommend that the starting amount of material, the starting amount of DNA to generate a complete
reliable DNA profile be somewhere between 500 and 1000 picograms of DNA.
Different kits vary. The least, the kit that requires the least amount of starting material
these days asks for 500 picograms as a minimum. Other kits ask for upwards of 1000 picograms.
You know what that works out to? Hereís what it works out to ñ itís about 100 to 200
cells is plenty enough to satisfy the minimum criteria for any of the commercially available
DNA profiling test kits that forensics labs use around the world right now. You know what
that means in simple terms? Quite plainly, a single fingerprint should provide, a typical
fingerprint should provide plenty enough DNA to generate a reliable, useful DNA profile.
Thatís how sensitive these tests are.
At a theoretical level, itís possible to imagine that you could get a DNA profile from
as little as a single cell. In practice the kits that are used to generate these DNA profiles
arenít using just a single cell, typically many dozens, ideally a couple of hundred.
The amount of material you might get from a single fingerprint. So, I promised just
a minute or two ago that Iíd help explain and get you comfortable with the idea of what
a picogram is; well letís talk about picograms here.
I tell you what, I am a biology professor. I am a molecular biologist and even still
I have to wrestle once in a while with what it is a picogram is because we donít talk
in those terms that often; certainly not in our day to day lives walking down the street.
So letís put this in fairly simple terms. A packet of sugar ñ everybody knows what
a packet of sugar is, right. Many of you have probably encountered packets of sugar within
the last 24 hours, either sweetening your coffee or just finding some laying around
at a local restaurant that youíve been to.
But a packet of sugar, a standard packet of sugar weighs four grams. That means that it
contains within it four grams of sugar. One-fourth of four grams of sugar, pretty obviously this
isnít high level math here, but one-fourth of a four gram packet of sugar weighs a gram.
And thatís going to be our starting point then for talking about what a picogram is.
Because if you looked at that packet of sugar, you can break it up into quarters if you like,
but when youíre looking at that sugar closely, again, we all know that there are going to
be individual crystals of sugar there. Each of those individual crystals of sugar weighs
about a thousandth of a gram.
And scientists have a fancy way of talking about a thousandth of a gram, we call that
a milligram. Okay, so a thousand milligrams equals one gram. A thousand crystals of sugar
gets you in the ballpark of about a gram of sugar. Okay? But we need to delve in deeper
here. We canít stop with just talking about grams and milligrams; again, weíre looking
to figure out what a picogram is. If you divide it up, a crystal of sugar a thousand times,
used an unimaginably small knife and microscopes and such to get a grain of sugar or a crystal
of sugar chopped up that finely. That one thousandth of a crystal of a typical grain
of sugar out of a sugar packet that would weigh one nanogram.
A nanogram is a thousandth of a milligram. But weíre still not talking about picograms
because a picogram is a thousandth of a nanogram. How about that? If you do the math and you
figure it out that works out to a picogram is one billionth of a grain of sugar. Better
yet, one billionth of a gram of sugar. How about that? So thatís the kind of quantities
weíre talking about when weíre talking about generating DNS profiles. A billionth of a
gram, a billionth of a quarter packet of sugar is how much DNA weíre usually talking about
dealing with for generating DNA profiles.
Again a typical human cell has six to seven picograms of DNA within it; so six to seven
billionths of a gram. And a typical fingerprint will have in the ballpark of 100 cells, therefore
approximately 600 to 700 picograms of DNA. Even the most sensitive commercially available
DNA test kits right now are asking that, or at least recommending in their protocols that
a laboratory start with a minimum of 500 picograms of starting material. But at the very bottom
end here, these are still incredibly sensitive tests.
So, where have we been with all of this? Hereís the thing ñ DNA tests can get us reliable
DNA profile information from all sorts of different materials. We can start with blood.
We can start with saliva, *** and so forth. The bottom line is pretty much anything that
comes in contact with an individual has a pretty good potential for having DNA associated
with it. If youíre interested in finding out who it is that most recently wore a particular
article of clothing, you might simply go to the friction points on that article of clothing
ñ along the collarsí cuff for instance; or along the cuff of a sleeve where the garment
rubs up against a bit of exposed flesh. Those are commonly tested but pretty much anything
that comes in contact with that fabric has the potential to give rise to a DNA profile.
Weíve already seen it ñ toothbrushes, dental floss, combs ñ these are all potentially
good sources of DNA because those are things that come in contact with individuals, and
what comes in contact with an individual often has associated with it some DNA thatís suitable
for generating a DNA profile. But thereís another thing that needs to be borne in mind
here, and thatís this ñ the incredible sensitivity of DNA tests as we know them today is actually
a double edged sword.
We need to bear in mind that when we generate DNA profiles that we donít know anything
about the timeframe of the circumstances under which that DNA came to be associated with
the object thatís being tested. A few minutes ago I touched the podium in front of me and
I said ìGee look at that, Iíve left behind a fingerprint. I didnít notice that Iíd
left behind a fingerprint. Iím not missing any of those cells.î Right? Theyíre trash,
theyíre discarded. And yet consider this ñ what if at some point later today or in
the next week or two weeks a crime occurs somewhere near this podium; maybe in a completely
different room, Iím not sure how permanent the podium in front of me actually is. It
may well be used in many different settings over the course of a week.
If during the course of an investigation though somebody were to take DNA swabs, samples of
the podium in front of me, they may well find that my DNA profile is associated with this
particular podium. How about that? I may have had nothing at all to do with the crime. The
crime may have happened hours after Iíve been associated with this podium. By the same
token the crime may have happened hours before I came to be associated with this podium,
and yet, thereís my DNA profile.
If I get identified as a suspect in a particular investigation and my DNA is found associated
with a crime scene, I think we all know that the burden starts to shift towards me. Thatís
a shadow of suspicion that I donít think anybody wants to have cast upon them to have
to explain how it is that their DNA came to be associated with an article; especially
when you consider that again, I didnít have any knowledge or expectation that my touching
this podium might somehow, someday be involved with some type of investigation.
And I think itís easy to see then how it is that this could be a far reaching type
of problem for forensic DNA profiling. Again, I feel that I say this many times when Iím
talking with attorneys, but itís important to bear in mind that the presence of a DNA
profile on an object doesnít necessarily tell us anything about either the timeframe
or the circumstances under which that DNA came to be associated with what it is that
weíre testing. It could be that the DNA has been there for a few hours. It could be that
the DNA has been there for a few days, a few weeks, in some circumstances even a few years.
It could be that the DNA came to be there because it was deposited during the course
of the commission of a violent crime. It might also be that it came to be deposited there
simply by some very innocent contact that happened prior to, or even after, a crime
had occurred. How long can DNA persist? Well, DNA, like any chemical, is subject to degradation.
It can interact unfavorably with other things in the environment. But there are some DNA
samples that we know have persisted for many millions of years. So in the right circumstances,
DNA actually can be very stable, and itís certainly not unheard of to find that reliable,
useful DNA profile results can be generated from samples that are over 100 years old.
One interesting example of that that comes quickly to mind is associated with Butch Cassidy
and the Sundance Kid; mail bandits from mail trains back in the old west. Blood found associated
with one of the mail bags that they had stolen was used ultimately to identify the remains
of Butch Cassidy over 100 years after his death, his execution actually.
So, hereís the thing ñ when weíre talking about forensic DNA testing, we need to bear
in mind that thereís all sorts of things that might be suitable for our starting material
for generating a DNA profile, but because of the extraordinary sensitivity of the tests,
itís actually possible for DNA profiles to have this sort of double edged nature to them.
In one level the great sensitivity can be a very powerful tool for law enforcement for
generating investigative leads and probative evidence. In another sense the defense needs
to consider might there be some innocent explanations for how it is that a particular DNA profile
came to be associated with a crime scene.
That double edged nature of the tests becomes less of an issue when weíre talking about
larger and larger quantities of starting material, but for the past 10 years of so thereís been
an increasing tendency for crime laboratories to attempt to generate DNA profiles from ever
smaller amounts of starting material, and that is an increasing concern; this idea of
innocent transfer.
Alright, where are we going to go next with all of this? Iíve talked with you now for
about 40 minutes or so about how it is that DNA evidence can be and often is used in criminal
courts ñ prosecutors, defense, even post-conviction relief attorneys find that itís maybe one
of the most powerful tools in their arsenal for uncovering truth and helping guide along
jurors and judges to arriving at the appropriate conclusion for criminal cases.
How do we get there? Well ultimately weíre going to need to spend some time talking about
how it is that DNA profiles get generated. And that process is actually surprisingly
straightforward. Iíll tell you what, it will take me about 50 minutes to take you by the
hand and tell you how it is that we can generate a DNA profile. I think youíll find that we
have another video that speaks to that very topic. But in a nutshell, whatís going on
here is this ñ itís necessary right out of the gate to isolate and purify DNA from
crime samples. At that point an amplification step is going to be employed very briefly.
Itís involving PCR amplification.
Following that amplification of the regions of DNA that weíre interested in looking at,
thereís a size fractionation step. And at the end of all of that there is some computer
processing of the output of the data, and ultimately the need to break out some calculators
and do some multiplication and attach some statistical weights to the results that get
found. I understand that it may sound a little bit daunting coming in to this all naively.
Size fractionation ñ that sounds complicated in and of itself; PCR amplification, whatís
going on with that. But I assure you that the whole process from beginning to end can
easily be accomplished in the course of a day, and it wouldnít take more than about
45 or 50 minutes to explain to you in fairly fine detail how it is that those DNA profile
results ultimately end up getting generated.
But, thatís for another time. For now, let me just recap briefly what it is Iíve been
talking with you about, about how it is that DNA gets used in court cases within the US
and abroad. Itís become a very favorite tool of criminal prosecutors all over the world.
Itís also popular amongst defense attorneys, and increasingly so, in fact, I would like
to encourage defense attorneys to be even more open to the idea of using DNA tests in
the same way that prosecutors have found them to be so useful.
Very often it seems in my interactions with defense attorneys they are a little bit afraid
when they hear that DNA tests are involved, but I think itís fair to say that the prosecutors
were afraid when they first started working with DNA evidence. Itís become one of their
best friends over the past 20 years, and I think with a similar familiarity, defense
attorneys will find that itís one of their best friends as well.
And letís not forget about cases like the one out of Louisiana that I mentioned earlier
ñ the 300th exoneration involving DNA test results. DNA testing is something that can
provide very powerful tools as part of post-conviction relief as well. And whenever weíre talking
about DNA tests I hope that one of the first things that comes to mind is these tests are
truly the most sensitive forensics tests that are available to us at this present time.
In fact itís hard to imagine tests being more sensitive then DNA testing results are.
Again, our bodies are made of trillions of cells; pretty much any one of those cells
has got the potential to give rise to a DNA profile. And by the time weíre talking about
just a few dozen cells, certainly by the time weíre talking about 100 or 200 cells, weíre
clearly in the range where weíve got enough material to generate a reliable DNA profile.
So thereís great sensitivity; that sensitivity particularly at the lower ends comes with
a price. Thereís often concerns that are associated with how it is that the profile
came to be associated with this sample, and when it is it came to be associated with the
sample. But in terms of sensitivity, nothing has DNA testing beat for forensic scientists.
And as Iíve just suggested, with that sensitivity, thatís a double edged sword. And whenever
weíre talking about DNA profile matches and linking individuals to particular crime scenes
and crimes, itís going to be important to think about alternative interpretations and
alternative theories about how it is that the DNA came to be associated with the sample
that has actually been tested. Bottom line, DNA test results need to be interpreted with
caution; particularly when weíre dealing with small amounts of starting material.
Alright, so that brings me to the point where I think we can wrap things up for this particular
topic. Bottom line, DNA is widely used in US Courts and around the world. Prosecutors
love it. Defense attorneys are beginning to embrace it more and more. Post-conviction
attorneys have found it to be one of their single best tools for securing post-conviction
relief. Literally hundreds of individuals now have been exonerated with DNA test results.
Itís an amazing technology. It has great promise. Itís actually something that can
be better still. And in the course of the next video or two in this series, what youíll
see is not just how it is that DNA profiles get generated, but how it is that statistical
weights get attached to them; and ultimately, how it is that we can make DNA testing better
than it is at the present time.
So Iím Dan Krane and Iíve enjoyed talking with you for the last 45 minutes or so about
DNA testing. And I hope that youíll look at some of the other videos in this series
to see some of these other interesting aspects of forensic DNA testing.