手机数据的滥用

　　The two towers

　　两个发射塔

　　Junk science is putting innocent people in jail

　　伪科学正将无辜的人民推向囹圄。

　　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，在奥勒冈州波特兰市，一名妓女被勒死。警方逮捕了丽莎·罗伯茨，受害者的前任情人，且被拘留两年多等候审判。在审判前不久，检察官通过律师，告诉罗伯茨小姐，由威瑞森通讯公司收集到的发射塔数据，即她的手机网，精确地显示了她在案发时的位置。她的律师回忆道，检察官说罗伯茨小姐有可能是“被定位”到公园，而且不久受害者一丝不挂，遭到性侵犯的尸体也是在那被发现的。罗伯茨被判25年有期徒刑。她接受一项协议：承认有罪并服刑15年。

　　手机数据的滥用.jpg

　　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，指控罗伯茨的高科技证据是假的。常规情况来说，发射塔的数据可以收集手机在相当宽范围内的信号，但却无法对其“定位”。要定位则需由特殊的三塔“三角网”，而这依旧无法显示你曾去过哪。罗伯茨小姐花了十年才洗脱罪名。拘留12年后，2014年5月28日，她出狱了，无犯罪记录。

　　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.

　　华盛顿原告律师协会史蒂芬·詹森说，手机发射塔定位数据广泛用于法庭。去年，美国法院和执法部门向美国电话电报公司发出了37,839张传票、法院命令以及对其定位数据的搜查令。该公司称，截止到今年六月底，已经收到30,886张了。

　　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.

　　詹森说，在过去几年，辩护律师已经引进越来越多的专家来质疑发射塔证据。北达科他州公设辩护律师Ryan Bialas说，大部分警官和律师对手机网运行原理“摸不着头脑”。在警匪题材的剧集中，类似“现场犯罪调查”让陪审团信以为科学提供的证据几乎是不会出错的。但是发射塔的数据远没有检察官说的那样精准。

　　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是一家位于弗吉尼亚州的取证公司。该公司老板迈克尔·谢里证实，在20多个涉及发射塔证据的审判中，检察官误解了该项技术。通常情况下，该技术只是确定手机连接上了附近的发射塔。事实上，在同一个地方连续两次拨号有可能会连接两个不同的发射塔：一个是附近的，另一个可能是几英里远的。谢里先生补充道，辩护律师有时会使用相同的“伪科学”技术来支持不在场证明。

　　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准备的一份证词中写道，本文引用的罗伯茨案件，其发射塔可服务范围可能是方圆20英里（即32公里）。手机连接发射塔有以下几个影响因素：附近的树叶有多浓密，墙有多厚，附近的车是大是小，水域是大是小，以及是否正常使用手机。这些影响因素从来就不会记录备份。

　　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.

　　卫报数字取证的拉里·丹尼尔，在一本即将付梓的书中这样写道，....法庭上使用的大部分发射塔证据都是无效的。丹尼尔先生已经帮助检察官和辩护律师做过近240次咨询工作，他发现其中有一半都有问题。即使如此，发射塔的记录在法庭上还是有一席之地的，丹尼尔先生说，这些记录可以证明手机在宽广地区的移动情况，比如不相邻城市之间。

　　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.

　　防止发射塔数据的滥用并不困难，但费用昂贵。卫报数字取证局使用该项技术花费每小时250美元。无罪释放罗伯茨小姐的法官责怪她的律师没能质疑手机证据，而这一证据本可以在陪审团那被推翻的。现在她的律师已经死了。波特兰市联邦辩护律师办公室首席调查员William Teesdale抱怨鲁德·昂德希尔检察官就罗伯茨一案，并未提出罗伯茨小姐手机上事发的另一通电话，因为那一通电话有可能将罗伯茨定位在犯罪现场。手机连接上了另一个不同的发射塔，这个塔离公园很远，而距离目击者看到罗伯茨小姐的地点很近。检察官昂德希尔拒绝回应。