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Kopi Sianida : Are The Police Right OR Is It Just A New Form of The Prosecutor Fallacy?

Pernah dengar tentang Prosecutor Fallacy?

Prosecutor Fallacy mudahnya adalah kesalahan penggunaan konsep peluang ketika ingin menunjukkan peluang seorang tersangka bersalah.

Misal :
Terjadi pembunuhan dan pelaku meninggalkan bukti berupa darah, sedemikian sehingga darah ini ternyata hanya ada 1 di setiap 1000 orang. Lalu ada si X yang darahnya matching dengan darah yang ada di TKP.
Maka oleh prosecutor dibilang wah ini darah cuma ada 1:1000, artinya si X ini peluang tidak bersalahnya cuma 1:1000 alias 0.1% alias peluang salahnya 99.9%.

Waw this prosecutor brought probability to the court!!!

BUT… this logic is sooo far from flawless. Kenapa? Karena penggunaan teorema Bayes di sini definisi peluangnya terbalik.

Peluang 0.1% ini adalah peluang darah matching jika diketahui tidak bersalah {P(A|B)}, sedangkan yang kita ingin tau adalah berapa sih peluang tidak bersalah jika diketahui darah matching {P(B|A)}.

Lalu apa hubunganny ama kasus kopi sianida? Prosecutor fallacy mengajarkan kita jangan sampai kesesatan berfikir ini terbawa ke pengadilan dan akhirnya membawa imbas jelek bagi siapa pun yang terlibat, dalam kasus ini polisi. Punya firasat bahwa si X adalah pelaku ya sah-sah saja, tapi jangan sampai firasat ini nutupin bukti atau keganjilan-keganjilan lain yang ada di TKP.

Kasus Prosecutor fallacy yang terkenal ada namanya The Sally Clark case, di mana Sally dituduh membunuh 2 bayi nya yg baru lahir, hanya karena seorang pakar bilang kalo peluang bayi dalam satu keluarga meninggal karena SIDS adalah 1:73juta, waw artinya peluang kalo Sally yang bunuh anaknya besar sekali. TAPI sayangnya si pakar menghitung peluang ini salah, tapi di tahun 1998 ga ada yang menangkap kesesatan cara mendapatkan 1:73juta ini, akhirnya Sally ditangkap tahun 1999, dan baru dibebaskan tahun 2003 ketika profesor dibidang matematika menghitung ulang peluang ini, Sally meninggal tahun 2007 karena problem psikis, dan jadi alkoholic.

See, this is dangerous!

Sama seperti kasus kopi sianida, si J datang duluan ke TKP, si J yang beliin kopi, si J bayar kopi terburu-buru, jadi pasti si J nih yang bersalah! O…o… This kind of logic is dangerous, tapi yah ga tau juga sih, karena mungkin saja kasus ini sebenernya se-simple itu.

Trus ada yang nyamain kasus ini dengan kasus di Conan, emang sih di Conan pake sianida juga dan emang sih di situ yg bunuhnya yang beliin kopi.

Trus gue inget ada tv series barat jadul taun 2006-an judulnya Boston Legal episode The Verdict, di mana di kasus ini polisi udah yakin banget kalo Scott membunuh seorang wanita hanya karna ada psikiatris yg ngasi rekaman terapi antara dia dan scott, di mana di rekaman itu scott bilang kalo dia mimpi ngebunuh si wanita. Kasus langsung masuk pengadilan. Di sini pengacara scott keren abis, dia bisa “membujuk” semua juri yg hadir bahwa scott ini ga bersalah, karena ada namanya “Reasonable doubt”, ini “bujukan” dari jaksa penuntut dan pengacara scott di akhir cerita :

Jaksa penuntut : Did anybody fall for that? First, he said the husband did it. Then, it was all those other men she was having an affair with. Then, I can’t be sure, but I think he actually seemed to accuse the father, at least briefly. Oh, and let’s not forget Lincoln Meyer, the neighbor. He wanted you to think that he was the killer. And then finally, in the most desperate and transparent attempt of all, he goes after Scott’s mother. And she played along perfectly, didn’t she? “I want an attorney. I assert my Fifth Amendment right.” Gee, that ought to give them all reasonable doubt. The evidence, all of it, points to one person being in the house—the defendant, a sick twisted, psychologically infirm young man, loaded with anger, self-loathing. He confessed to his therapist he had compulsions of killing her. Gee, I wonder who could have done it. If any of you were fooled by the defense lawyer’s ridiculous Perry Mason theatrics, then shame on you.

Pengacara Scott: Shame on you? How ‘bout shame on the police for investigating nobody else but Scott Little? As soon as they saw a video of Scott talking about killing Marcia Hooper, it was “Case Closed” for them. Could they not have looked at the husband? He had motive; he was there; he has no real alibi; he made no attempt to save her. Could they not have looked at Lincoln Meyer, the card-carrying nut-job from next door? He was obsessed with Marcia Hooper. She had to get a restraining order to keep him away. His flowers were found in the room where she was murdered. And yes, Barbara Little. Let’s face it: Love obsessions rarely occur in a vacuum. Could she not have loved him just as much? Her whole life is her son. The idea of him falling into the clutches of another woman—? Why was that house so clean of prints? The killer will typically wipe clean just what he or she has touched. But if she didn’t know what Scott had previously touched, she would have cleaned everything. How can any of us be sure here? As for physical evidence, the only thing the prosecution can establish is that Scott Little made love to Marcia Hooper the night of the murder. Well, he told them that. He came forward, as innocent people tend to do, and volunteered the information. The only reason they arrested him was because of a video and an opinion proffered by an eccentric therapist who runs around telling people he’s kissed movie stars he’s never even met. This can’t turn on his credibility. Talk about reasonable doubt. Reasonable doubt! Come on. It could have been him, could have been him, could have been her. This whole case screams, “Reasonable doubt,” which is typically the case when the police don’t investigate.

Isn’t that line beautiful? Soo smooth.

And let’s not forget this quote from Patrick Jane The Mentalist – No wife should glow at her husband’s funeral“, in this case : “No husband(family/friend) should glow at his wife’s funeral”.

So am i saying the husband did it? No.
Jessica? No.

I don’t know, i’m not an expert in this.

See ya!

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