TED日本語 - スコット・フレイザー: なぜ目撃証言はあてにならないか


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TED日本語 - スコット・フレイザー: なぜ目撃証言はあてにならないか

TED Talks


The problem with eyewitness testimony


Scott Fraser






The murder happened a little over 21 years ago, January the 18th,1991, in a small bedroom community of Lynwood, California, just a few miles southeast of Los Angeles. A father came out of his house to tell his teenage son and his five friends that it was time for them to stop horsing around on the front lawn and on the sidewalk, to get home, finish their schoolwork, and prepare themselves for bed. And as the father was administering these instructions, a car drove by, slowly, and just after it passed the father and the teenagers, a hand went out from the front passenger window, and -- "Bam, Bam!" -- killing the father. And the car sped off.

The police, investigating officers, were amazingly efficient. They considered all the usual culprits, and in less than 24 hours, they had selected their suspect: Francisco Carrillo, a 17-year-old kid who lived about two or three blocks away from where the shooting occurred. They found photos of him. They prepared a photo array, and the day after the shooting, they showed it to one of the teenagers, and he said, "That's the picture. That's the shooter I saw that killed the father."

That was all a preliminary hearing judge had to listen to, to bind Mr. Carrillo over to stand trial for a first-degree murder. In the investigation that followed before the actual trial, each of the other five teenagers was shown photographs, the same photo array. The picture that we best can determine was probably the one that they were shown in the photo array is in your bottom left hand corner of these mug shots. The reason we're not sure absolutely is because of the nature of evidence preservation in our judicial system, but that's another whole TEDx talk for later. (Laughter)

So at the actual trial, all six of the teenagers testified, and indicated the identifications they had made in the photo array. He was convicted. He was sentenced to life imprisonment, and transported to Folsom Prison.

So what's wrong? Straightforward, fair trial, full investigation. Oh yes, no gun was ever found. No vehicle was ever identified as being the one in which the shooter had extended his arm, and no person was ever charged with being the driver of the shooter's vehicle. And Mr. Carrillo's alibi? Which of those parents here in the room might not lie concerning the whereabouts of your son or daughter in an investigation of a killing?

Sent to prison, adamantly insisting on his innocence, which he has consistently for 21 years.

So what's the problem? The problems, actually, for this kind of case come manyfold from decades of scientific research involving human memory. First of all, we have all the statistical analyses from the Innocence Project work, where we know that we have, what,250,280 documented cases now where people have been wrongfully convicted and subsequently exonerated, some from death row, on the basis of later DNA analysis, and you know that over three quarters of all of those cases of exoneration involved only eyewitness identification testimony during the trial that convicted them. We know that eyewitness identifications are fallible.

The other comes from an interesting aspect of human memory that's related to various brain functions but I can sum up for the sake of brevity here in a simple line: The brain abhors a vacuum. Under the best of observation conditions, the absolute best, we only detect, encode and store in our brains bits and pieces of the entire experience in front of us, and they're stored in different parts of the brain. So now, when it's important for us to be able to recall what it was that we experienced, we have an incomplete, we have a partial store, and what happens? Below awareness, with no requirement for any kind of motivated processing, the brain fills in information that was not there, not originally stored, from inference, from speculation, from sources of information that came to you, as the observer, after the observation. But it happens without awareness such that you don't, aren't even cognizant of it occurring. It's called reconstructed memories. It happens to us in all the aspects of our life, all the time. It was those two considerations, among others -- reconstructed memory, the fact about the eyewitness fallibility -- that was part of the instigation for a group of appeal attorneys led by an amazing lawyer named Ellen Eggers to pool their experience and their talents together and petition a superior court for a retrial for Francisco Carrillo. They retained me, as a forensic neurophysiologist, because I had expertise in eyewitness memory identification, which obviously makes sense for this case, right? But also because I have expertise and testify about the nature of human night vision.

Well, what's that got to do with this? Well, when you read through the case materials in this Carrillo case,one of the things that suddenly strikes you is that the investigating officers said the lighting was good at the crime scene, at the shooting. All the teenagers testified during the trial that they could see very well. But this occurred in mid-January, in the Northern Hemisphere, at 7 p.m. at night. So when I did the calculations for the lunar data and the solar data at that location on Earth at the time of the incident of the shooting, all right, it was well past the end of civil twilight and there was no moon up that night. So all the light in this area from the sun and the moon is what you see on the screen right here. The only lighting in that area had to come from artificial sources, and that's where I go out and I do the actual reconstruction of the scene with photometers, with various measures of illumination and various other measures of color perception, along with special cameras and high-speed film, right? Take all the measurements and record them, right? And then take photographs, and this is what the scene looked like at the time of the shooting from the position of the teenagers looking at the car going by and shooting. This is looking directly across the street from where they were standing. Remember, the investigating officers' report said the lighting was good. The teenagers said they could see very well. This is looking down to the east, where the shooting vehicle sped off, and this is the lighting directly behind the father and the teenagers. As you can see, it is at best poor. No one's going to call this well-lit, good lighting, and in fact, as nice as these pictures are, and the reason we take them is I knew I was going to have to testify in court, and a picture is worth more than a thousand words when you're trying to communicate numbers, abstract concepts like lux, the international measurement of illumination, the Ishihara color perception test values. When you present those to people who are not well-versed in those aspects of science and that, they become salamanders in the noonday sun. It's like talking about the tangent of the visual angle, all right? Their eyes just glaze over, all right? A good forensic expert also has to be a good educator, a good communicator, and that's part of the reason why we take the pictures, to show not only where the light sources are, and what we call the spill, the distribution, but also so that it's easier for the trier of fact to understand the circumstances. So these are some of the pictures that, in fact, I used when I testified, but more importantly were, to me as a scientist, are those readings, the photometer readings, which I can then convert into actual predictions of the visual capability of the human eye under those circumstances, and from my readings that I recorded at the scene under the same solar and lunar conditions at the same time, so on and so forth, right, I could predict that there would be no reliable color perception, which is crucial for face recognition, and that there would be only scotopic vision, which means there would be very little resolution, what we call boundary or edge detection, and that furthermore, because the eyes would have been totally dilated under this light, the depth of field, the distance at which you can focus and see details, would have been less than 18 inches away.

I testified to that to the court, and while the judge was very attentive, it had been a very, very long hearing for this petition for a retrial, and as a result, I noticed out of the corner of my eye that I thought that maybe the judge was going to need a little more of a nudge than just more numbers.

And here I became a bit audacious, and I turned and I asked the judge, I said, "Your Honor, I think you should go out and look at the scene yourself."

Now I may have used a tone which was more like a dare than a request - (Laughter) - but nonetheless, it's to this man's credit and his courage that he said, "Yes, I will." A shocker in American jurisprudence.

So in fact, we found the same identical conditions, we reconstructed the entire thing again, he came out with an entire brigade of sheriff's officers to protect him in this community, all right? (Laughter) We had him stand actually slightly in the street, so closer to the suspect vehicle, the shooter vehicle, than the actual teenagers were, so he stood a few feet from the curb toward the middle of the street. We had a car that came by, same identical car as described by the teenagers, right? It had a driver and a passenger, and after the car had passed the judge by, the passenger extended his hand, pointed it back to the judge as the car continued on, just as the teenagers had described it, right? Now, he didn't use a real gun in his hand, so he had a black object in his hand that was similar to the gun that was described. He pointed by, and this is what the judge saw.

This is the car 30 feet away from the judge. There's an arm sticking out of the passenger side and pointed back at you. That's 30 feet away. Some of the teenagers said that in fact the car was 15 feet away when it shot. Okay. There's 15 feet.

At this point, I became a little concerned. This judge is someone you'd never want to play poker with. He was totally stoic. I couldn't see a twitch of his eyebrow. I couldn't see the slightest bend of his head. I had no sense of how he was reacting to this, and after he looked at this reenactment, he turned to me and he says, "Is there anything else you want me to look at?"

I said, "Your honor," and I don't know whether I was emboldened by the scientific measurements that I had in my pocket and my knowledge that they are accurate, or whether it was just sheer stupidity, which is what the defense lawyers thought - (Laughter)- when they heard me say, "Yes, Your Honor, I want you stand right there and I want the car to go around the block again and I want it to come and I want it to stop right in front of you,three to four feet away, and I want the passenger to extend his hand with a black object and point it right at you, and you can look at it as long as you want." And that's what he saw. (Laughter)

You'll notice, which was also in my test report, all the dominant lighting is coming from the north side, which means that the shooter's face would have been photo-occluded. It would have been backlit. Furthermore, the roof of the car is causing what we call a shadow cloud inside the car which is making it darker. And this is three to four feet away.

Why did I take the risk? I knew that the depth of field was 18 inches or less. Three to four feet, it might as well have been a football field away. This is what he saw. He went back, there was a few more days of evidence that was heard. At the end of it, he made the judgment that he was going to grant the petition for a retrial. And furthermore, he released Mr. Carrillo so that he could aid in the preparation of his own defense if the prosecution decided to retry him.

Which they decided not to. He is now a freed man. (Applause)


This is him embracing his grandmother-in-law. He -- His girlfriend was pregnant when he went to trial, right? And she had a little baby boy. He and his son are both attending Cal State, Long Beach right now taking classes. (Applause)

And what does this example -- what's important to keep in mind for ourselves?

First of all, there's a long history of antipathy between science and the law in American jurisprudence. I could regale you with horror stories of ignorance over decades of experience as a forensic expert of just trying to get science into the courtroom. The opposing council always fight it and oppose it.

One suggestion is that all of us become much more attuned to the necessity, through policy, through procedures, to get more science in the courtroom, and I think one large step toward that is more requirements, with all due respect to the law schools, of science, technology, engineering, mathematics for anyone going into the law, because they become the judges. Think about how we select our judges in this country. It's very different than most other cultures. All right?

The other one that I want to suggest, the caution that all of us have to have, I constantly have to remind myself, about just how accurate are the memories that we know are true, that we believe in? There is decades of research, examples and examples of cases like this, where individuals really, really believe. None of those teenagers who identified him thought that they were picking the wrong person. None of them thought they couldn't see the person's face. We all have to be very careful. All our memories are reconstructed memories. They are the product of what we originally experienced and everything that's happened afterwards. They're dynamic. They're malleable. They're volatile, and as a result, we all need to remember to be cautious, that the accuracy of our memories is not measured in how vivid they are nor how certain you are that they're correct.

Thank you. (Applause)

その殺人事件は約21年前に起こりました 1991年1月18日 舞台は ロスから数キロしか離れていない カリフォルニア州リンウッドの 小さなベッドタウンです 一人の父親が 自宅の前で遊んでいた 彼の10代の息子とその5人の友人達に そろそろ遊ぶのを止めて家に帰って 宿題をして寝る準備をするように 促すために家から出てきました 父親が子ども達に声をかけているとき 1台の車がゆっくりと近づいてきました そして父親と子ども達の横を通り過ぎると 助手席の窓から手が伸びて・・・ バン!!バン!!父親を射殺しました 車はそのまま去りました

警察は すばらしく素早い動きをしました 札付きどもの中から 24時間以内に容疑者を特定しました フランシスコ・カリヨ 17歳 銃撃現場から 数ブロックのところに 住んでいた少年です 警察は彼の写真を手に入れて面割りの写真に混ぜたのです それを事件翌日に 目撃者の少年の一人に見せました 「この写真の男です。 銃撃犯はこの男です。」

予審判事にとってはこれだけ聞けば十分で カリヨ氏は第一級殺人で 被告席に立つことになりました 裁判が始まる前の捜査で 残る5人の少年たちも 同じ写真で面割りをしました これら顔写真の中で 最もよく判別しやすい顔写真は おそらく皆さんから見て左下の写真でしょうね 私たちが絶対的確信を持てない理由は 司法制度における証拠保存の本質に関わる問題ですが またそれは 別の TEDx の機会に (笑)

裁判では 6人の目撃者の少年全員が 写真を指差して 証言をしました 彼は有罪となり終身刑を宣告され フォルサム刑務所に収監されました

どこもおかしなところはありません 十全な捜査と公正な裁判ですすべて順調に進みました ただ凶器の銃は見つかりませんでした 犯行に使われた車は特定されず 誰も 犯人の車を運転していた者として 起訴されることはありませんでした カリヨ氏のアリバイですが 殺人事件の捜査において 容疑者の両親のアリバイ証言はあてにできません

刑務所に入れられてから21年間 彼は断固として無実を訴えてきました

何が問題か? この類の事件ではとりわけ問題があることが 記憶に関わる何十年もの研究から知られています イノセンス・プロジェクトには 誤って有罪判決を受けた死刑囚を含む囚人について 後のDNA鑑定による冤罪証明がなされた 250以上の事例に関して さまざまに統計解析を行いました そのうちの実に4分の3の事例は 有罪判決を下した裁判において 目撃証言だけを根拠としています 目撃証言による人物の特定はあてになりません

もう一つの問題は 人間の脳の持つ様々な機能についての 興味深い点から生じます 簡単に言うと 脳は「空白」を嫌います 最もよい観察環境においてさえ 我々は目の前で起こっている出来事を 断片として扱いそれぞれの断片を 脳の様々な場所にしまい込みます では不完全で断片的な記憶で 自分の経験を思い出さねばならないとき 何が起こるか? 無意識のうちに 何の動機づけすらなくても脳は 当初は記憶されていなかった情報を 推測や憶測 目撃した時点よりも後に得た情報を基に 補ってしまうのです これは人が全く気付かない内に起こります いわば「再構成された記憶」です これは生活のあらゆる場面でいつも起きています 再構成された記憶と 目撃証言の不確かさの2点を 考慮することをきっかけに すご腕の法律家であるエレン・エガースに― 率いられた弁護士たちは 経験と才能を持ちより 上訴審にフランシスコ・カリヨの 再審請求を行うことにしました 私は目撃証人の記憶について 専門知識を有する 神経生理学者として裁判に 参加することになりました持ってこいの役回りですね また暗いところでの人間の視覚についても 専門家として証言しました

カリヨ氏の事案とどう関係するでしょうか 事件の記録で注目すべきことのひとつは 捜査員たちが銃撃の現場の明るさについて 十分に明るかったと証言していたことです 少年たちも全員がよく見えたと裁判で証言をしています しかしこの事件が起こったのは 1月中旬の北半球 夜の7時です 私は銃撃のあった当夜の 現地の太陽と月の位置を計算しました 夕暮れ時はとうに過ぎた時刻で その日は月も出ていませんでした つまり事件当夜の現場で 太陽や月からの光は皆無 現場の明かりは 人工的な光源のみによるもののはずです そこで私は現場におもむき 光度計を手に状況の再現を試みました 照明や 色の認識に関わる条件を― 変えながら特別なカメラと高感度フィルムで記録しました あらゆる条件を試みて 全てを記録しました そして写真にも残しました 当時の現場の見取り図に基づき 少年たちがいた場所から 車が走りながら銃撃するのを見るとどうなるでしょう これは 少年たちのところから 通りの向かいをまっすぐ見た写真です 捜査官の報告では 光は十分とのことでしたね また少年たちもよく見えたと言っていました この東向きの写真は 犯人の車が走り去った方向を撮りました 父親と少年たちの背後の照明の 状況の写真です ご覧の通り控えめに言っても乏しい光です これでは誰も十分な明るさとは言わないでしょう 実際の光はこの写真の通りです 私は法廷で証言するためにこの写真を撮りました というのも国際的な照度の単位であるルクスや 石原式色覚検査のスコアについて 非専門家に伝えたいときに 一枚の写真は千の言葉を費やすよりも効果的だからです そうした抽象概念について 科学的側面に詳しくない人たちに話すときは まさに百聞は一見に如かずなのです 視覚の正接についての話なんて 実に退屈でぼうっとなりますよ 法廷における優れた専門家は教えることや コミュニケーションに秀でていなければなりません 写真で見せることで 光源の場所や光の届き方だけでなく 事実を検証する人にとって 状況をわかりやすくするのです これらは私が実際に証言の時に使った写真ですが それよりも重要なのが科学者として私が 計測した光度計の示した値です その結果を使って 実際の状況下で 肉眼で何が見えるかを推測できます 同じ太陽と月の条件で 同時刻など条件を揃えて 私が現場で計測した値から 顔の認識に不可欠な色の認識については はなはだ心許ない夜目の状態だったと言えます ものの輪郭をはっきりと捉えることも ほとんどできない状況です さらにこの光の下では瞳孔は開いた状態で 50センチ未満の奥行きについてしか 目の焦点を合わせて細部を見ることはできません

私は法廷でこのことを証言しました 判事は本当に熱心に耳を傾けてくれましたが 再審請求の大変長い 意見聴取を経てきていたこともあり 数字だけではなく 何かもう一押しが必要なのではないかと なんとなく感じました

そこで私は大胆にも 判事に向かってこう願い出ました 「裁判官 ご自身で一度現場をご覧になっては如何でしょうか?」

お願いというより少し挑戦的な口調だったかもしれませんが・・・(笑) にもかかわらず判事は誇りと勇気をもって言いました 「行きましょう」 これはアメリカの法の世界では驚くべきことです

そして実際に私たちが事件と全く同じ状況下で 現場の状況をふたたび再現し 判事は郡保安官に護衛され 仰々しい車列を組んで現れました(笑) 我々は判事に 実際に目撃者の少年たちが立っていた位置よりも 少し銃撃犯の車に近い位置に立ってもらい 彼は道路に向かって歩道の縁石から数十センチの位置に立っていました そして少年たちが証言したとおりの車を走らせました 運転席と助手席に人が乗っており 判事の横を通り過ぎざま助手席の同乗者が 判事に向けて手を伸ばし 手は判事を指したまま車は走り去ります 少年たちの証言に従って行いました 実物の銃ではなく 証言された銃に似せた黒いものを 手にしていました これがその時に判事が見た光景です

これは判事から約9メートル先で 助手席の窓からこちらに向かって腕が出ています これは約9メートルですが 約4.5メートルと証言した少年もいました これで約4.5メートルです

この時点で私は少し心配になっていました この判事は絶対にポーカーの相手にはしたくない人物です まったく感情が表に出ないのです眉一つ動かさず 首を傾げることもありません まったく反応を読み取れませんでした この再現の後に 彼は私に向き直って尋ねました 「他に何か見せたいものはある?」

手元にある科学的な計測データと 正確な知識に励まされたのか あるいは被告弁護人の思うとおり 私の完全な愚かさからか(笑) 私は言いました 「はい裁判官 そちらでお立ちください 車をもう一回りさせて目の前 約1メートルのところで止めます そのまま助手席から腕を出して 黒い物体をあなたに向けますから お気の済むまでそれをご覧下さい。」 これが裁判官の目にした光景です(笑)

皆さんもお気づきでしょうし私も報告書に書きましたが 光は主に北側からさしています つまり銃撃犯の顔は逆光になって見えないのです さらに車の屋根が影になって 車内をさらに暗くしています これは約1メートル先の見え方です

なぜわざわざこんなことをしたのか? 視界が50センチもないことを知っていたからです それでは1メートル先というのは フットボールグラウンドの向こう側と同じことです 判事はこれを見て 法廷に戻りました 証言を聴く時間がまだ数日残っていましたが 結局判事は再審請求を受理しました さらに検察が再び彼を訴追する場合 その弁護に備えられるよう カリヨ氏を釈放しました

検察は彼を再び訴追することなく 彼は晴れて自由の身となりました(拍手)


義理の祖母を抱きしめているところです 裁判中に妊娠していた彼の恋人は 男の子を生んでいました 彼は今 息子と一緒に カリフォルニア州立大のロングビーチ校で学んでいます(拍手)

さて この事例で 我々が心に留めておくべきことは何でしょうか?

アメリカの法曹界では法学と科学は 長い間犬猿の仲でした 何十年と法廷に関わってきた専門家としての経験の中で 法廷に科学を持ち込もうとして 相手にされないというひどい話は尽きません 相手方の法律家たちがいつも頑として反対するのです

ここで提起したいのは 我々が政策や手続きを通じて もっと法廷に科学を取り入れる必要性を 支持することです それに向けての大きな一歩は 全く失礼を言うようですが ロースクールにおいて 科学・技術・工学・数学の 必修科目としての比重を高めることです 皆そこで学んで裁判官になるのですから 我々がこの国で裁判官を選ぶ方法は 他の国々とは大きく違っています

もう一つ注意しなければならないと思うことは 私自身もいつも意識していることですが 我々が真実だと信じて疑わない 記憶についてです 何十年にも及ぶ研究があり 今回のような事例は実にたくさんあります すなわち一人ひとりは 心底信じています証言した少年たちは誰も 間違った人物を選んでいるとは・・ 犯人の顔を見られていないなどとは・・ 全く思っていませんでした 私たちは皆注意する必要があります 私たちの記憶は全て再構成された記憶なのです それは元々の経験と その後に起こった全ての出来事によって作られ 変化し続けるものです そして時には悪い作用も生み出します またそれは不安定で我々はみな注意深くあらねばなりません 我々の記憶はいかに鮮明であっても 正しいとどれほど信じていても その正確さは測れないのです


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