評論
打印
The abuse of mobile-phone data
手機數據的濫用
The two towers
兩個發射塔
Junk science is putting innocent people in jail
偽科學正將無辜的人民推向囹圄。
SOMEONE strangled a prostitute in Portland, Oregon in 2002. The police arrested Lisa Roberts, the victim's ex-lover, who spent more than two years in custody awaiting trial. Shortly before the trial the prosecutor told Ms Roberts, via her lawyer, that tower data collected by Verizon, her mobile-telephone network, showed precisely where she was at the time of the murder. As her lawyer recalled, the prosecutor said Ms Roberts could be “pinpointed” in a park shortly before the victim's naked and sexually assaulted corpse was found there. She was told she faced 25 years to life in prison. She accepted a deal to plead guilty and serve 15 years.
2002年，在奧勒岡州波特蘭市，一名妓女被勒死。警方逮捕了麗莎·羅伯茨，受害者的前任情人，且被拘留兩年多等候審判。在審判前不久，檢察官通過律師，告訴羅伯茨小姐，由威瑞森通訊公司收集到的發射塔數據，即她的手機網，精確地顯示了她在案發時的位置。她的律師回憶道，檢察官說羅伯茨小姐有可能是“被定位”到公園，而且不久受害者一絲不掛，遭到性侵犯的尸體也是在那被發現的。羅伯茨被判25年有期徒刑。她接受一項協議：承認有罪并服刑15年。
But the high-tech evidence against her was bunk. Routinely collected tower data can place a mobile phone in a broad area, but it cannot “pinpoint” it. That would require a special three-tower “triangulation”, which cannot reveal past locations. It took a decade for Ms Roberts's guilty plea to be thrown out. On May 28th she left prison, her criminal record clean, after nearly 12 years in custody.
然而，指控羅伯茨的高科技證據是假的。常規情況來說，發射塔的數據可以收集手機在相當寬范圍內的信號，但卻無法對其“定位”。要定位則需由特殊的三塔“三角網”，而這依舊無法顯示你曾去過哪。羅伯茨小姐花了十年才洗脫罪名。拘留12年后，2014年5月28日，她出獄了，無犯罪記錄。
Mobile-phone-tower location data is widely used in court, says Steven Jansen of the Association of Prosecuting Attorneys in Washington, DC. Last year America's courts and law-enforcement agencies served 37,839 subpoenas, court orders, and search warrants for location data just to one phone company, AT&T. This year's figure had already climbed to 30,886 by the end of June, the company says.
華盛頓原告律師協會史蒂芬·詹森說，手機發射塔定位數據廣泛用于法庭。去年，美國法院和執法部門向美國電話電報公司發出了37,839張傳票、法院命令以及對其定位數據的搜查令。該公司稱，截止到今年六月底，已經收到30,886張了。
In the past couple of years defence lawyers have brought in more experts to challenge tower evidence, says Mr Jansen. Most police officers and lawyers have “no clue” how phone networks function, says Ryan Bialas, a North Dakota public defender. Cop shows like “CSI” give juries the idea that scientific evidence is almost infallible. But tower data is far less accurate than prosecutors sometimes claim.
詹森說，在過去幾年，辯護律師已經引進越來越多的專家來質疑發射塔證據。北達科他州公設辯護律師Ryan Bialas說，大部分警官和律師對手機網運行原理“摸不著頭腦”。在警匪題材的劇集中，類似“現場犯罪調查”讓陪審團信以為科學提供的證據幾乎是不會出錯的。但是發射塔的數據遠沒有檢察官說的那樣精準。
Location, location, location
定位，定位，定位
Cherry Biometrics, a Virginia forensics firm, has testified in more than 20 trials where tower evidence was being used. In all of them, says Michael Cherry, the boss, prosecutors misunderstood the technology. Often they would assert that mobile phones connect to the nearest tower. In fact, two calls dialled consecutively from the same spot may connect to two different towers: one close by, the other many miles away. Defence lawyers sometimes use the same “junk science” to support alibis, adds Mr Cherry.
Cherry Biometrics是一家位于弗吉尼亞州的取證公司。該公司老板邁克爾·謝里證實，在20多個涉及發射塔證據的審判中，檢察官誤解了該項技術。通常情況下，該技術只是確定手機連接上了附近的發射塔。事實上，在同一個地方連續兩次撥號有可能會連接兩個不同的發射塔：一個是附近的，另一個可能是幾英里遠的。謝里先生補充道，辯護律師有時會使用相同的“偽科學”技術來支持不在場證明。
The tower cited in Ms Roberts's case could have handled calls from as far as 20 miles (32km) away, according to a deposition prepared by Cherry Biometrics. Which tower a phone connects with depends on such factors as how thick the nearby foliage and walls are, the size of nearby cars and bodies of water, and how well the handset is working. None of this information is usually recorded.
Cherry Biometrics準備的一份證詞中寫道，本文引用的羅伯茨案件，其發射塔可服務范圍可能是方圓20英里（即32公里）。手機連接發射塔有以下幾個影響因素：附近的樹葉有多濃密，墻有多厚，附近的車是大是小，水域是大是小，以及是否正常使用手機。這些影響因素從來就不會記錄備份。
Without it, much of the tower evidence presented in court is useless, writes Larry Daniel of Guardian Digital Forensics in a forthcoming book on the subject. Mr Daniel has found errors in nearly half of the 240 consulting jobs he has done for prosecutors and defence lawyers. Even so, tower records do have a place in court, says Mr Daniel: they can generally prove that a handset has moved between broad areas such as non-adjacent cities.
衛報數字取證的拉里·丹尼爾，在一本即將付梓的書中這樣寫道，....法庭上使用的大部分發射塔證據都是無效的。丹尼爾先生已經幫助檢察官和辯護律師做過近240次咨詢工作，他發現其中有一半都有問題。即使如此，發射塔的記錄在法庭上還是有一席之地的，丹尼爾先生說，這些記錄可以證明手機在寬廣地區的移動情況，比如不相鄰城市之間。
Preventing the misuse of tower data should not be hard, though it can be expensive. Guardian Digital Forensics charges $250 an hour for its expertise. The judge who freed Ms Roberts faulted her lawyer, now dead, for failing to challenge mobile-phone evidence that would probably have collapsed before a jury. William Teesdale, the chief investigator for Portland's federal defender's office, complains that the prosecutor, Rod Underhill, never addressed another call on Ms Roberts's phone around the same time as the one that supposedly placed her at the murder scene. It connected to a different tower, farther away from the park and closer to a spot where Ms Roberts had been seen by a witness. Mr Underhill refused to comment.
防止發射塔數據的濫用并不困難，但費用昂貴。衛報數字取證局使用該項技術花費每小時250美元。無罪釋放羅伯茨小姐的法官責怪她的律師沒能質疑手機證據，而這一證據本可以在陪審團那被推翻的。現在她的律師已經死了。波特蘭市聯邦辯護律師辦公室首席調查員William Teesdale抱怨魯德·昂德希爾檢察官就羅伯茨一案，并未提出羅伯茨小姐手機上事發的另一通電話，因為那一通電話有可能將羅伯茨定位在犯罪現場。手機連接上了另一個不同的發射塔，這個塔離公園很遠，而距離目擊者看到羅伯茨小姐的地點很近。檢察官昂德希爾拒絕回應。
