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You've Been Lied to About DNA Evidence - Video học tiếng Anh
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You've Been Lied to About DNA Evidence
You've Been Lied to About DNA Evidence
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Субтитры (508)
0:00
- Thank you to Squarespace for supporting PBS.
0:02
- I immediately think, oh my God, I'm being framed.
0:08
This is impossible.
0:09
I, I cannot explain how this could be.
0:13
Meredith's DNA should not be on the knife
0:17
that was found at my boyfriend's house.
0:20
- Amanda Knox spent four years in prison for a murder
0:24
that she didn't commit.
0:25
The media circus was honestly pretty insane, all
0:29
because some tiny invisible molecules seemed
0:33
to say that she did it.
0:35
- Her pleas fell on deaf ears.
0:37
Amanda Knox is now a convicted killer.
0:43
A lot of magical claims were made about how,
0:46
if you find DNA, that it's unquestionable
0:49
and it definitively proves guilt.
0:52
- Forensic DNA technologies become so sensitive
0:55
that today a single cell's worth
0:57
of genetic material can be detected at a crime scene
1:00
and identified to solve that crime.
1:03
Or at least that's how it's supposed to work, but...
1:07
Just because there's DNA doesn't
1:10
mean we know what happened.
1:13
- What happens if we push that science beyond its limits?
1:17
What happens when police start chasing ghosts?
1:27
Hey, smart people, Joe here.
1:29
Forensic DNA technology has totally revolutionized
1:32
criminal investigation.
1:34
We have the ability to collect, processed
1:37
and identify invisible, beyond microscopic molecules
1:41
that are left behind at crime scenes,
1:43
which is honestly mind blowing.
1:46
We're all probably somewhat aware of what DNA forensics is,
1:50
and for many people I'm betting that's thanks to TV.
1:57
Shows like CSI created this perception.
2:00
Researchers literally call it the CSI effect,
2:02
where the public and more importantly, people on juries came
2:06
to see DNA evidence as basically magic: swab a crime scene,
2:10
run it through a computer, and boom, you got your killer.
2:14
Juries kind of tend to treat DNA
2:16
as infallible proof rather than one piece
2:19
of a much messier puzzle.
2:21
- That DNA doesn't lie.
2:24
I think it's important
2:25
and pretty interesting to learn
2:26
how DNA forensics actually works.
2:29
And as we're about to see it isn't always as infallible
2:33
as we've been told.
2:36
I guess this is a true crime show today.
2:40
On a sunny spring day in 2007,
2:43
two German police officers were taking a break in their car.
2:46
They had the doors open.
2:47
It was a really nice day,
2:49
but moments later,
2:50
they were both shot in the head from behind.
2:53
One officer, 22-year-old Michelle Kiesewetter didn't survive.
2:58
Investigators diligently swabbed the scene
3:01
to collect any traces of the killer's DNA,
3:03
and they got a hit. To their shock.
3:06
It matched DNA from multiple other crime scenes.
3:09
This suspect's DNA was connected to drug deals,
3:12
burglaries, and assaults in multiple
3:14
countries across Europe.
3:16
In addition to a half dozen other murders. A serial killer
3:21
and super criminal was haunting Europe.
3:23
The strangest part, all DNA evidence pointed to the fact
3:27
that the killer was a she.
3:29
Despite the fact
3:30
that only one in six serial killers are thought to be women,
3:34
she was tied to several different accomplices, none
3:36
of whom would give her up to police authorities,
3:39
figured they were all just too scared of her to snitch.
3:42
Police eventually linked her DNA
3:44
to 40 different crime scenes across Europe going back
3:47
to 1993.
3:49
She was dubbed the Phantom of Heilbronn
3:52
because no one ever saw her commit these crimes,
3:55
but her DNA was everywhere.
3:58
But fast forward to April, 2008, as evidence is piling up,
4:02
investigators announced we're closing in on her
4:05
except there was no her to close in on
4:09
because the killer that they were chasing wasn't real.
4:14
Everything started to fall apart when the Phantom's DNA
4:17
showed up in a French case involving a burned body.
4:21
Now, the police had a hunch that the body belonged
4:23
to a man who'd gone missing,
4:25
but this person had entered the country seeking asylum.
4:27
So investigators had his fingerprints on
4:30
that asylum application,
4:31
but when they swabbed those fingerprints from his asylum
4:34
application to serve as a reference to ID the burned body,
4:38
the Phantom's DNA turned up in that sample: female DNA.
4:43
This didn't make any sense.
4:45
The swab of DNA wasn't even from a crime scene,
4:49
and it should have only contained male DNA.
4:53
A horrifying realization began to hit the investigators.
4:57
They had indeed been hunting a phantom,
5:00
but that phantom was DNA contamination.
5:04
- So the DNA's strength, like all of our strengths,
5:09
is also its weakness.
5:11
- That's Dr. Greg Hampikian, a forensic DNA expert.
5:16
- I've gotten DNA out of, you know,
5:18
400 year old mummy bones.
5:20
It's very persistent.
5:21
If it's taken care of, it lasts quite well,
5:24
even at room temperature. Every year, in every lab there are
5:27
contamination events.
5:30
- In the Phantom's cases, the contamination turned out
5:32
to be from the cotton swabs used
5:34
to collect samples at the crime scenes.
5:37
Those swabs had come from a factory in Bavaria
5:41
where they'd been contaminated with DNA from a woman
5:44
who worked there at the factory.
5:46
Her DNA matched the phantom profile
5:49
at all of those crime scenes.
5:50
A few stray molecules had led police on a wild goose chase
5:54
across Europe for years.
5:57
- It's very easy to move DNA
5:59
and we should never confuse identification
6:04
information, which is, "who is the ultimate source of this?"
6:09
with questions about activity.
6:12
How did the DNA get here?
6:14
- Of course, I had to ask Amanda
6:16
what she thought of this case.
6:17
- She's like, what? I just make cotton.
6:21
I, I mean what, what incredible story to talk about
6:24
how like narratives form
6:27
and like completely take over the public imagination
6:31
and they have a completely different explanation.
6:34
Like, ah, wow.
6:35
- Instead of just focusing on the identity,
6:38
which is the only thing that DNA can actually tell you,
6:43
the police made up a story about activity, about
6:46
what had happened, what happened to get the DNA there.
6:50
This was the fatal flaw of the Phantom
6:53
of Heilbronn investigation.
6:54
They invented a serial killer.
6:57
And that supposedly magical
6:59
DNA evidence? Wasn't so magical here. To understand
7:02
how a cotton swab fooled the entire German police force,
7:07
we need to understand what forensic DNA analysis actually is
7:11
and why it's both incredibly powerful
7:14
and incredibly fragile.
7:16
So how's it supposed to work? Let's solve a murder, shall we?
7:21
Imagine this kitchen knife was collected at a crime
7:24
scene and it's believed
7:26
to be the murder weapon. To catch the killer,
7:29
we've swabbed the knife hoping that the murderer left
7:31
behind some traces of bodily materials like skin cells,
7:35
hair, blood or semen, because all of those contain DNA.
7:39
Now, importantly, we also have a swab from the victim
7:42
to make sure that any DNA
7:43
that we find isn't just the dead person's DNA.
7:45
Now, DNA from a single skin cell contains a person's
7:49
entire genome, billions of DNA letters
7:53
--their full genetic blueprint.
7:55
But investigators today don't usually read all of that DNA
7:58
to get an ID.
8:00
Sequencing whole genomes is getting mind-blowingly cheap,
8:03
and may be how forensic DNA testing is done in the future.
8:07
But today we're gonna use a different cool trick.
8:09
To read a genetic fingerprint
8:11
that is currently the gold standard in forensics.
8:14
Our genome has thousands of genes that carry instructions
8:18
for making stuff that keeps us alive.
8:20
But the vast majority of our DNA does not make stuff.
8:25
And in those giant In-between regions,
8:28
there are these short little stretches
8:30
where DNA sequences repeat back to back.
8:33
They're called short tandem repeats or STR's.
8:36
We have lots of different STRs throughout our genome
8:39
and each STR can vary in
8:42
how many repeats it contains And sequencing just 20
8:46
of them can create a DNA profile
8:48
that can identify one unique individual.
8:51
To show you what I mean, let's take a look at the DNA
8:54
profile of our victim.
8:56
Now at the first STR spot,
8:58
the little DNA repeating sequence is AGAT.
9:03
Now the victim has one allele
9:04
or version of the STR with five repeats
9:08
and another allele with nine repeats.
9:12
That's because s STR are something that we inherit from mom
9:15
and dad, just like all of our other DNA sequences.
9:18
So it's possible to have two different alleles
9:21
for any STR sequence.
9:23
- They say ‘ah-le-le’ in Italian, sorry, alleles in English.
9:27
- The second STR spot consists of repeating TCATs.
9:31
Our victim only has an allele
9:34
for 12 repeats at this STR
9:37
because they inherited the same one: 12 repeats from both
9:41
parents, mom and dad.
9:43
Now the third STR spot consists of repeating ATTs
9:46
and our victim has alleles for eight and 10 repeats.
9:50
We do this on and on up to the 20 STRs
9:53
that make up a full genetic profile.
9:55
These 20 STRs are standard across forensic investigations,
10:00
and they form the basis of something called CODIS,
10:03
the massive DNA database maintained by the FBI.
10:06
All of the cells in the victim's body have their unique
10:09
combination of STR repeats except their eggs
10:13
or sperm, which only have half of them.
10:15
But the most important thing, the thing
10:17
that makes forensic DNA identification possible is
10:21
that the victim has a different combination
10:23
of STR repeats than the murderer does.
10:26
And not just that they have a different DNA profile than any
10:29
other person does.
10:31
Check this out. So two people may share the same number
10:34
of repeats at one STR, maybe even two,
10:38
but across all 20 STR sites,
10:41
there is less than a one in a trillion, trillion chance
10:46
that they have all of the same repeats at all
10:49
of the same spots unless they're identical twins.
10:52
Those are pretty good odds
10:53
that any DNA fingerprint is totally unique.
10:57
So let's go back to our murder weapon.
11:00
The swabs will have picked up DNA from our victim,
11:03
and now that we have the STR profile from our victim,
11:07
we can easily separate it from any other STRs
11:10
that we may find in the mix, any other DNA profiles,
11:14
we find? It might be the murderer.
11:16
We can then run those STR profiles against those
11:19
of any suspects to see if there's a match
11:21
or run it through CODIS to search
11:24
for matches from this giant database of criminals
11:26
and other crime scenes.
11:28
And we found another DNA profile
11:31
that matches someone near the case.
11:33
So does that mean it's our murderer? Well, not so fast.
11:38
First I need to tell you about Lucas Anderson
11:41
5,600 miles away from Ohio Bron in Santa Clara
11:45
County, California.
11:46
Lucas Anderson was having a very bad day. In December, 2012.
11:51
His DNA was found in a sample taken from under the
11:53
fingernails of a wealthy California investor who'd been tied
11:57
up and killed during a home break-in. Lucas's name popped up
12:00
as the match to that DNA
12:02
because he was in the database due
12:04
to his past criminal record.
12:06
He also had memory problems from an old head injury
12:09
and he routinely blacked out due to alcoholism.
12:11
So he honestly couldn't say for sure that he was innocent.
12:15
To the prosecutors, this looked like an open and shut case.
12:18
The DNA analysis worked as it should.
12:21
It provided an unambiguous match to a known criminal,
12:25
and there was plenty of circumstantial evidence
12:26
to write a story of what happened that night.
12:29
Lucas was sent to jail on a murder charge,
12:32
which could carry the death penalty.
12:34
But as his lawyers combed through evidence trying
12:37
to save him from death row,
12:38
they found something pretty important.
12:41
The night of the murder, Lucas had been in the hospital
12:44
for alcohol intoxication after collapsing at a store.
12:47
So how could his DNA be at the scene
12:50
of the crime when he was in a hospital bed?
12:53
Miles away?
12:55
His defense team interviewed the paramedics
12:57
who picked him up, and it turned out
12:59
that they were the same paramedics who responded
13:01
to the nine one one call at the scene of the murder,
13:04
and they had processed the victim's body.
13:07
- Human DNA can transfer as a solid,
13:10
a liquid or as an aerosol.
13:13
- Lucas's case was one of DNA transference.
13:16
Tiny traces of DNA had traveled from Lucas
13:20
to the paramedics to the victim.
13:23
But because our scientific technology is so sensitive,
13:26
that was more than enough
13:28
to yield a positive match to Lucas.
13:30
And we don't know for sure,
13:32
but his DNA may have hitched a ride on a pulse oximeter.
13:35
You know those little things they put on your finger
13:37
that the medics had used on both men?
13:40
- We call it activity level proposition.
13:44
Can you tell when it's directly by a hand?
13:47
No, there's no way to tell
13:50
but there are people in my field who will testify that way,
13:53
and I think it's shocking and fraudulent.
13:56
- When do people stop asking,
13:58
"Is there an innocent explanation for this DNA?"
14:01
"Are we taking shortcuts to automatically assume the guilt
14:04
of the DNA and not asking that question?"
14:07
- Thankfully, Lucas was eventually freed, but only
14:10
after he spent five months in jail,
14:13
and the prosecutors weren't the ones asking the questions.
14:16
The science did exactly what it was supposed to.
14:20
Lucas's DNA genuinely was there,
14:23
and that was enough for them to construct a narrative about
14:26
what that DNA meant, A narrative
14:28
that could have sent an innocent man to death row.
14:31
And this is nothing compared to
14:33
what happened with Amanda Knox.
14:37
20-year-old Amanda was studying abroad in Perugia, Italy
14:41
in the fall of 2007. She was living
14:44
with her roommate Meredith Kercher,
14:45
who just started dating a local student named Rafaelle Sollecito.
14:49
On November 2nd,
14:50
the unthinkable happened. Meredith's body was found in her bedroom
14:54
of their shared apartment. She'd been sexually assaulted
14:57
and brutally murdered with a knife.
15:00
Now, the DNA and fingerprints
15:01
of a man named Rudy Guede were found all over the crime scene.
15:05
He had fled to Germany.
15:07
He was arrested and ultimately charged with the murder.
15:09
But during the investigation, Amanda was subjected
15:13
to an endless series of harsh interrogations,
15:16
ultimately resulting in a coerced confession.
15:19
Amanda and her boyfriend were arrested
15:21
and also charged with Meredith's murder.
15:25
- It affected the way DNA was then processed afterwards.
15:29
So the arrests came before the DNA came.
15:32
I think it took two or three weeks for the DNA
15:35
that they collected at the crime scene to be processed.
15:38
And by that time, they already had arrests.
15:40
They had already announced to the world
15:42
that the case was closed.
15:43
They already had a narrative about what had happened
15:46
to my roommate, which turned out to be very, very wrong.
15:50
I'm a 20-year-old kid who believes
15:52
that when the actual evidence is processed at the crime
15:56
scene, it will reveal the truth that I had nothing to do
15:59
with this crime and that I'll be released and let go.
16:02
- But that's not what happened.
16:05
Investigators found a torn off bra clasp from Meredith's
16:08
room and a kitchen knife in Raphael's apartment. Forensic
16:12
analysis identified Raphael's DNA on the bra clasp
16:16
and Amanda's DNA on the knife handle
16:19
and Meredith's DNA on the knife plate.
16:22
Amanda was convicted of murder
16:24
and sentenced to 26 years in prison,
16:27
thanks in large part
16:28
to this supposedly slam dunk DNA evidence.
16:32
I mean her DNA on a knife handle,
16:34
a victim killed with a knife.
16:37
What else could that mean?
16:39
Well, as we've seen, DNA evidence isn't always as clear
16:43
and unambiguous as TV would lead you to believe.
16:48
- You have DNA experts at war with each other
16:52
who are each claiming to have authority over the truth.
16:56
It was just incredibly frustrating for me to have
17:00
to sit there and listen
17:01
to people construct a reality out of whole cloth, all
17:06
for the sake of the narrative.
17:08
- Four years passed before the court agreed to hear Amanda
17:11
and Raphael's appeal
17:13
and reexamine the evidence with a panel
17:15
of independent forensic experts.
17:17
- Our crime scene was processed by forensic experts twice,
17:21
once in the immediacy of the crime being discovered.
17:25
But then after those samples had been processed
17:28
and none of it implicated me or my boyfriend
17:32
or anybody in the crime, they went back in 46 days later
17:36
to try to find new forensic evidence
17:39
to implicate us in the crime,
17:40
and they have completely upended our house
17:44
and contaminated it completely.
17:47
- The only piece of DNA evidence tying Raphael
17:49
to the crime was found in that problematic second sweep
17:54
after evidence had been mixed and thrown around all
17:56
but guaranteeing that the evidence would be contaminated.
18:00
Oh, and the knife?
18:02
- I did a little work on Amanda Knox's case.
18:05
- I love Greg. He's the best.
18:07
- Yeah, really it was just that knife for Amanda.
18:11
A single cell can make it look like a suspect was
18:15
on a piece of evidence.
18:16
When we saw the electropherograms, it was clear to us
18:19
that the DNA was at such a low level.
18:22
How are the Italians looking way
18:24
below anything I do in my research lab?
18:27
- The trace of DNA that is on it is so minuscule
18:30
that it can't be attributed to anyone
18:32
- I knew right away.
18:34
This was suspicious.
18:35
The guidelines say you need to separate evidence
18:38
and reference samples.
18:39
You do all of the evidence first.
18:41
When the evidence is finally processed,
18:43
you bring the reference samples into the lab.
18:45
You never bring 'em into the lab before that.
18:47
- Reports indicated that the knife blade samples were
18:50
processed in the middle of 50 samples
18:53
of reference material from Meredith.
18:55
Traces of her DNA could have easily contaminated the
18:59
knife blade samples.
19:00
And considering that modern forensic DNA technology is
19:03
so sensitive, it can pick up on just a few
19:05
cells worth of DNA.
19:07
Not following careful contamination procedures is
19:09
incredibly risky.
19:11
It was another case of confirmation bias.
19:14
Investigators had constructed a grizzly narrative
19:18
of this crime
19:19
and pushed the science well beyond its safe limits
19:22
until they found data that agreed with their conclusions.
19:26
This is the opposite of good science.
19:29
- The independent experts found the exact same findings
19:32
that my defense team found.
19:33
- We showed in the end it was probably transfer
19:37
contamination
19:38
and not the result of a criminal act. That took four years
19:42
of Amanda being in prison
19:44
to convince the Supreme Court in Italy.
19:47
- I'm really interested
19:48
to see a world in which the forensic evidence comes
19:52
so quickly that it can be the thing
19:54
that guides the narrative construction as opposed
19:57
to the thing that tries
19:58
to justify an already established narrative.
20:02
- In a world like the one Amanda describes with faster,
20:06
better forensic science,
20:08
how many other people would never have been arrested
20:11
for those crimes they didn't commit?
20:14
- Anytime you introduce a new process,
20:17
you introduce a new field of error.
20:19
That's always gonna be true no matter
20:21
how good the instrument is, no matter
20:23
how good the training is,
20:24
- Because science is evolving at a rapid pace,
20:28
especially science around DNA, it's so important
20:31
that we open up opportunities to appeal decisions
20:35
that were based on bad science in the past.
20:38
- There's a couple of states that have passed laws that say,
20:42
if the science you were convicted by has now been superseded
20:46
by better science that corrects the old view,
20:50
you have a right to retest evidence.
20:53
Most states don't have that law,
20:55
- And so innocent people are sitting behind bars
20:57
with no legal avenue for proving their innocence.
21:00
- How many people have been convicted with sloppy DNA?
21:03
How many times has that happened?
21:05
I bet it's happened a lot of times.
21:06
- The beauty of science is that it recognizes
21:10
that it has its own limitations.
21:12
It's an evolving practice and it's willing to revisit
21:15
and reevaluate certain calculations.
21:18
The problem is that legal systems are not
21:21
designed like that.
21:22
And I think that the legal system would do well
21:25
to take on a more scientific mindset of: "it is possible
21:29
that we got this wrong."
21:31
- We could all use a little more scientific mindset.
21:34
Something that kept coming up in these conversations
21:36
and cases was how often humans fall victim
21:39
to constructing stories
21:42
and then looking for evidence
21:43
that supports those stories rather than following the
21:46
evidence and building the story based only
21:50
on what can be proven.
21:51
This is what science demands, right?
21:54
With technology that's now sensitive enough
21:56
to get a DNA profile from a single cell,
21:58
it's more important than ever
22:00
to avoid weaving elaborate stories from a molecule like DNA.
22:05
Because DNA can really only answer the question of
22:09
who not how.
22:11
With the Phantom, Lucas, Amanda,
22:14
and who knows how many other cases, the DNA never lied.
22:19
We just didn't ask the right questions. Stay curious.
22:23
- Science is so interesting.
22:26
- Happy Earth Month.
22:28
PBS is celebrating Earth Month by releasing a ton
22:31
of great content across our channels,
22:33
diving deep into our amazing planet,
22:36
like the latest release from Deep Look, all about
22:39
bioluminescence, a video
22:42
that we would give an... a glowing review?
22:46
Links to that video and the full Earth Month
22:47
playlist are in the description.
22:50
And a thank you to Squarespace for supporting PBS.
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If you'd like to join our community
23:55
and get to see videos like this one live
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before everybody else
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and a lot of other cool behind the scenes perks, head over
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to the link down in the description
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and we'll see you in the next video.
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The researcher...blbllp... literally...
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We can then run those STR profriles.
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Profiles...
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Let's go...
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BANG!
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I meant to do that.
