so what happened here did you see the
car drive on through the ice did you see
it go through the ice
did you see the person get out of the
vehicle was it an accident was it a
homicide and the bodies still in the car
was it an attempted suicide we don’t
really know do we and that’s the thing
we weren’t there to see it what we’re
left with are the remnants of the
activity of interest and we have to
piece those together to try to make
sense out of what happened when I teach
forensic science I teach it as a
historical science like archaeology
paleontology or geology and that’s
because we’re all doing the same thing
we’re all taking what’s left over from
events we’re interested in I’m trying to
put them back together and make sense of
them to reconstruct past events we’re
trying to make the absent present in a
sense all of these Sciences center
around sort of start from a novel
written by Voltaire about a character
named Tzadik and the book is called the
book of fate Tzadik is a wanderer and
he’s walking through the woods one day
and some of the Queen’s retainers burst
up and through the trees and see him and
say have you seen the Queen’s dog and he
says small spaniel long years just had
puppies limp and the left front paw yeah
that’s it have you seen it I don’t even
know what Queen had a dog then some of
the King’s staff burst through the trees
looking for the King’s prize stallion
that’s missing and Tzadik says excellent
gallop er small hubs about five feet
tall tale about three and a half feet
long gold on the bridle silver shoes
they’re like exactly which way did it go
I haven’t seen any horses today so they
immediately assume that he’s lying and
that he’s a thief and they arrest him
and they drag him in front of a judge as
I dig explains his methodology which I
will do to you
and he’s released and has other
adventures in the book but this is
important because this is the fur
written example of what we could call a
forensic philosophy and that’s important
because forensic science even though
it’s critical to our criminal justice
system doesn’t have an overarching
philosophy it doesn’t have a guiding set
of principles and that’s important
Thomas Kuhn said that one of the things
that differentiates science from
pseudoscience is an internal corrective
mechanism that is the ability to spot
your errors correct them and make sure
they don’t happen again and that’s what
forensic science needs what we do is we
construct reconstruct past criminal
events right that’s what we’re using our
abilities for now we don’t get a perfect
picture we don’t get the name and
address of the of the assailant what we
get are as Freud notes slight and
obscure traces and those are what we
have to put together and the burden is
on us to be able to interpret those
George Cuvier was a pioneer of
paleontology the study of fossils used
proxy data to develop what he referred
to as the principle of correlation of
parts and what that means is if we find
a fossil and it has large canines sharp
teeth we can assume that it’s a
carnivore and that the rest of the body
will follow suit Cuvier is principle is
based on interrelated elements of a
system so big teeth means a carnivore
and the rest of the body will look like
a carnivore in forensic science we do
this routinely we see a fingerprint we
assume there’s a finger and behind the
finger as a person that happens all the
time
but we don’t think about it like that
another example that we use in forensic
science borrowed from geology that we
don’t know we borrowed from geology is
called uniformitarianism and that’s a
big word that simply means that natural
phenomena do not change in scope
intensity or effect over time way to
paraphrase that is that the present is
the key to the past
and what that means is if we look and
see how volcanoes act today and the type
of information that they produce today
then what we’re doing is seeing that
process in action and we can apply that
to the interpretation of volcanoes that
erupted 200 years ago 200 million years
ago it doesn’t matter we can we can make
these interpretations almost out without
regard to time in forensic science we do
the same thing we test fire bullets on
the range today and we compare those two
bullets from the crime scene two days
two weeks two months two years ago again
we can make these comparisons almost
without regard to time now another
principle that we borrow from geology
without really knowing it is called the
principle of superposition again a big
word all that means is younger stuff is
on top older stuff is on the bottom as
you can see in this picture of sideling
Hill from Maryland I used to drive past
there all the time and always thought it
was a great example you can see that the
older layers of rock are below the
younger layers which are on top this
only makes sense
if I spill coffee in a napkin the napkin
was there first otherwise the coffee
couldn’t be spilled on it so the napkins
slightly older than the coffee even if
only by a second or so likewise at a
crime scene when blood is shed the
surface that lands on had to be there
first otherwise the blood couldn’t be
shed on top of it now you might be
thinking wow that’s a really simple idea
but crime scenes are complex
environments and many crime scenes have
been misinterpreted for a lack of
knowledge about simple procedures like
this
another one that we borrow from geology
is called the principle of lateral
continuity and that means that materials
in a layer are continuous until an
object interrupts them so like cutting a
cake for example now in forensic science
we use the principle of lateral
continuity in a couple of ways one for
example let’s say there’s a broken pane
of glass from a window and we can fit it
back together like a
that tells us if we can do that that
that piece of glass was at one time a
continuous piece of glass lateral
continuity we can also do this with
evidence that’s transferred between an
assailant and a victim during an assault
so the the fibers that are transferred
between the two individuals if they had
no prior contact are taken as
indications of lateral continuity during
that assault and the more fibers we find
and the more different kinds of fibers
we find strengthen our interpretation of
that lateral continuity finally we have
absolute and relative chronology
relative chronology is simply saying one
thing is older or younger than another
pretty straightforward absolute
chronology is affixing a date or a time
some quantitative value to an event so
for example in forensic science if we
find a receipt from a hardware store
for a shovel on a bag of trash our box
of trash bags and some duct tape and
it’s dated the day before we find the
victim bagged taped and buried we call
that a clue that in fact happened during
one of my cases but using using those
those measures in forensic science are
important and you know we don’t think of
them that way I would be remiss talking
only about borrowed principles without
talking about one that comes from
forensic science itself Edmond Locard
who created the world’s first forensic
laboratory in Lyon France in 1914
developed this notion that now bears his
name
the Locard exchange principle states
that when two objects come into contact
information is exchanged pretty
straightforward you’re wearing boots you
step in the mud you get mud on your
boots you step on the floor you get mud
on the floor you get yelled at you have
tread on the boots that gets transferred
to the mud as an impression again pretty
straightforward but it’s the central
notion that powers forensic science
the only problem is
one principle isn’t enough and I’ll
explain why there are almost 2200 people
who have been wrongfully convicted and
were exonerated those are just the ones
we know about many of those people were
wrongfully convicted based on erroneous
notions of forensic science their lives
inner liberties were taken from them
what we need is that internal corrective
mechanism we need a set of guiding
principles a guiding philosophy to
forensic science we as a discipline need
to author our tomorrow so that we can
prevent future wrongful convictions and
allow innocent people to write to author
their own tomorrow’s thank you [Applause]
car drive on through the ice did you see
it go through the ice
did you see the person get out of the
vehicle was it an accident was it a
homicide and the bodies still in the car
was it an attempted suicide we don’t
really know do we and that’s the thing
we weren’t there to see it what we’re
left with are the remnants of the
activity of interest and we have to
piece those together to try to make
sense out of what happened when I teach
forensic science I teach it as a
historical science like archaeology
paleontology or geology and that’s
because we’re all doing the same thing
we’re all taking what’s left over from
events we’re interested in I’m trying to
put them back together and make sense of
them to reconstruct past events we’re
trying to make the absent present in a
sense all of these Sciences center
around sort of start from a novel
written by Voltaire about a character
named Tzadik and the book is called the
book of fate Tzadik is a wanderer and
he’s walking through the woods one day
and some of the Queen’s retainers burst
up and through the trees and see him and
say have you seen the Queen’s dog and he
says small spaniel long years just had
puppies limp and the left front paw yeah
that’s it have you seen it I don’t even
know what Queen had a dog then some of
the King’s staff burst through the trees
looking for the King’s prize stallion
that’s missing and Tzadik says excellent
gallop er small hubs about five feet
tall tale about three and a half feet
long gold on the bridle silver shoes
they’re like exactly which way did it go
I haven’t seen any horses today so they
immediately assume that he’s lying and
that he’s a thief and they arrest him
and they drag him in front of a judge as
I dig explains his methodology which I
will do to you
and he’s released and has other
adventures in the book but this is
important because this is the fur
written example of what we could call a
forensic philosophy and that’s important
because forensic science even though
it’s critical to our criminal justice
system doesn’t have an overarching
philosophy it doesn’t have a guiding set
of principles and that’s important
Thomas Kuhn said that one of the things
that differentiates science from
pseudoscience is an internal corrective
mechanism that is the ability to spot
your errors correct them and make sure
they don’t happen again and that’s what
forensic science needs what we do is we
construct reconstruct past criminal
events right that’s what we’re using our
abilities for now we don’t get a perfect
picture we don’t get the name and
address of the of the assailant what we
get are as Freud notes slight and
obscure traces and those are what we
have to put together and the burden is
on us to be able to interpret those
George Cuvier was a pioneer of
paleontology the study of fossils used
proxy data to develop what he referred
to as the principle of correlation of
parts and what that means is if we find
a fossil and it has large canines sharp
teeth we can assume that it’s a
carnivore and that the rest of the body
will follow suit Cuvier is principle is
based on interrelated elements of a
system so big teeth means a carnivore
and the rest of the body will look like
a carnivore in forensic science we do
this routinely we see a fingerprint we
assume there’s a finger and behind the
finger as a person that happens all the
time
but we don’t think about it like that
another example that we use in forensic
science borrowed from geology that we
don’t know we borrowed from geology is
called uniformitarianism and that’s a
big word that simply means that natural
phenomena do not change in scope
intensity or effect over time way to
paraphrase that is that the present is
the key to the past
and what that means is if we look and
see how volcanoes act today and the type
of information that they produce today
then what we’re doing is seeing that
process in action and we can apply that
to the interpretation of volcanoes that
erupted 200 years ago 200 million years
ago it doesn’t matter we can we can make
these interpretations almost out without
regard to time in forensic science we do
the same thing we test fire bullets on
the range today and we compare those two
bullets from the crime scene two days
two weeks two months two years ago again
we can make these comparisons almost
without regard to time now another
principle that we borrow from geology
without really knowing it is called the
principle of superposition again a big
word all that means is younger stuff is
on top older stuff is on the bottom as
you can see in this picture of sideling
Hill from Maryland I used to drive past
there all the time and always thought it
was a great example you can see that the
older layers of rock are below the
younger layers which are on top this
only makes sense
if I spill coffee in a napkin the napkin
was there first otherwise the coffee
couldn’t be spilled on it so the napkins
slightly older than the coffee even if
only by a second or so likewise at a
crime scene when blood is shed the
surface that lands on had to be there
first otherwise the blood couldn’t be
shed on top of it now you might be
thinking wow that’s a really simple idea
but crime scenes are complex
environments and many crime scenes have
been misinterpreted for a lack of
knowledge about simple procedures like
this
another one that we borrow from geology
is called the principle of lateral
continuity and that means that materials
in a layer are continuous until an
object interrupts them so like cutting a
cake for example now in forensic science
we use the principle of lateral
continuity in a couple of ways one for
example let’s say there’s a broken pane
of glass from a window and we can fit it
back together like a
that tells us if we can do that that
that piece of glass was at one time a
continuous piece of glass lateral
continuity we can also do this with
evidence that’s transferred between an
assailant and a victim during an assault
so the the fibers that are transferred
between the two individuals if they had
no prior contact are taken as
indications of lateral continuity during
that assault and the more fibers we find
and the more different kinds of fibers
we find strengthen our interpretation of
that lateral continuity finally we have
absolute and relative chronology
relative chronology is simply saying one
thing is older or younger than another
pretty straightforward absolute
chronology is affixing a date or a time
some quantitative value to an event so
for example in forensic science if we
find a receipt from a hardware store
for a shovel on a bag of trash our box
of trash bags and some duct tape and
it’s dated the day before we find the
victim bagged taped and buried we call
that a clue that in fact happened during
one of my cases but using using those
those measures in forensic science are
important and you know we don’t think of
them that way I would be remiss talking
only about borrowed principles without
talking about one that comes from
forensic science itself Edmond Locard
who created the world’s first forensic
laboratory in Lyon France in 1914
developed this notion that now bears his
name
the Locard exchange principle states
that when two objects come into contact
information is exchanged pretty
straightforward you’re wearing boots you
step in the mud you get mud on your
boots you step on the floor you get mud
on the floor you get yelled at you have
tread on the boots that gets transferred
to the mud as an impression again pretty
straightforward but it’s the central
notion that powers forensic science
the only problem is
one principle isn’t enough and I’ll
explain why there are almost 2200 people
who have been wrongfully convicted and
were exonerated those are just the ones
we know about many of those people were
wrongfully convicted based on erroneous
notions of forensic science their lives
inner liberties were taken from them
what we need is that internal corrective
mechanism we need a set of guiding
principles a guiding philosophy to
forensic science we as a discipline need
to author our tomorrow so that we can
prevent future wrongful convictions and
allow innocent people to write to author
their own tomorrow’s thank you [Applause]
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