我们对美墨边境死亡与监控问题长达15个月的调查始于一个简单的问题：为什么在旨在帮助追踪和逮捕越境者的政府监控塔附近，会有如此多的人死亡？

这个故事是《麻省理工科技评论》与《圣迭戈时报》合作推出的“镜头下的死亡”系列报道的一部分。两家新闻机构的记者在过去一年中审查了边境监控技术的失败之处，并挖掘了在边境地区死去的人们背后的故事。

为了回答这个问题，我们查阅了数千页的政府文件，多次前往边境实地走访，并对45多人进行了采访，包括现任和前任白宫顾问、总统任命官员、边境巡逻队员、法医验尸官、治安官、人道主义志愿者以及科技公司的员工。

我们的调查结果绘制出了首张关于边境监控塔附近死亡事件的全面地图和分析报告。以下是我们构建这份数据的过程、途中所做的决定，以及这些数据能够且不能告诉我们什么。

我们的数据

这项调查依赖于掌握移民死亡地点以及美国海关和边境保护局（CBP）监控塔的安装位置和时间。我们分析了可追溯至2015年的案例，从而涵盖了不同的边境政策、总统任期以及监控塔技术。

移民死亡事件

美墨边境被称为世界上最致命的陆地边界，边境巡逻队估计自2000年以来有超过1万人死于越境过程中——这一数字被广泛认为存在低估。然而，关于这些人何时何地死亡以及他们是谁的公开信息量差异巨大。有些遗体从未被发现，而对于那些被发现的遗体，也没有处理记录的国家统一协议。

如果我们要确认三个基本事实：该人是否被认为正在穿越边境、遗体在何处被发现以及该人大致何时死亡，我们才会将其纳入进一步分析的案例。

我们通过将其他组织（包括“不再死亡”、“人道主义边界”和“电子前沿基金会”）编制并共享的现有数据集，与我们从十多个机构自行获取的新记录进行合并，从而创建了我们的数据集。

德克萨斯州的公共记录申请

德克萨斯州是大多数现有移民死亡数据库中最缺失的一环。与亚利桑那州不同，它没有在线共享记录的举措；与新墨西哥州不同，它将各自的死亡调查留给各县自行处理。虽然一些县存在由少数敬业研究人员汇编的记录，但没有一份是全面或最新的。

我们确定了17个与我们调查相关的德克萨斯州县：卡尔伯森、杰夫戴维斯、普雷西迪奥、特雷尔、瓦尔韦尔德、基尼、马弗里克、迪米特、韦伯、萨帕塔、吉姆霍格、斯塔里、伊达尔戈、卡梅伦、肯尼迪、布鲁克斯和杜瓦尔。虽然在其他县也有移民死亡，但这些县没有监控塔覆盖的区域，因此被排除在外。

在这些县的大多数地方，由当地选举产生的行政法官（即治安法官）收集有关当地死亡事件的最全面信息。但是，向这些个别法官提交的记录申请可能会停滞数年（事实上，我们提交给治安法官的一些申请在提交一年多后仍未得到处理）。治安法官的报告有时会遗漏我们所需的现场或地点细节；有些治安法官甚至从不亲自前往移民死亡的现场，而是通过FaceTime与现场的急救人员通话，正式宣布该人死亡。

新墨西哥州桑兰公园与墨西哥普埃尔托德阿纳普拉之间的边境墙。GETTY IMAGES

《麻省理工科技评论》转而于2025年7月起向这17个县的治安官办公室提交了记录请求。这些机构通常在发现死亡事件时最先到达现场，其报告可能包含更多关于遗体被发现地点的详细信息。但依赖治安官的记录意味着我们的分析低估了德克萨斯州移民死亡人数，因为它没有包括由当地或州警察处理的任何死亡案例。

在我们提交申请后，为了获取这些记录（如果最终能获取到的话），我们不得不几乎每天致电各办公室。有些机构免费提供了记录。其他县则收取300至1,300美元不等的费用来处理我们的请求。各县警告称，他们的记录不完整，在搬迁过程中、治安官交接期间，有数量不明的记录丢失、受损、被毁或遗失。

这些延误因大多数机构不记录死者是否被认为是在越境时死亡而加剧。尽管一些县的规定允许官员追踪更细致的其他情况细节；例如，萨帕塔县的报告设有复选框以表明入室盗窃中是否有珠宝被盗，而卡梅伦县的报告则设有复选框以表明窃贼是否通过烟囱进入。由于缺乏快速识别移民死亡案例的方法，办公室不得不手动提取记录，这使得过程更慢、成本更高且更容易出错。

我们从这17个县中的14个县收到了可用的记录（尚未收到迪米特县或杜瓦尔县的记录，而马弗里克县的办公室收取的每条记录费用高昂到令人望而却步）。

机构通常向我们发送每个个案的警察报告，总计超过4,000页的记录。其中一些是手写文件。

除了肯尼迪县、韦伯县和伊达尔戈县的报告外，我们手动提取了相关信息。对于这三个发送了大量记录的县，我们使用通过API访问的Anthropic的Claude来检查每个案例报告并提取遗体被发现地点的坐标；然后我们手动抽查这些案例批次以验证AI的准确性。机构从2025年7月到2026年2月陆续向我们发送记录，且大多数未说明其记录更新至哪一天。

我们通常信任机构发送的是他们认为涉及移民死亡的案例，因为他们对每个案例拥有最多的信息。但有些记录显然表明并非如此（例如，指出某人死在家中），我们将这些案例排除在外。

数百个案例因缺乏足够信息让我们确定遗体被发现地点而被从我们的分析中移除。在不到100个案例中，虽然未列出坐标，但描述足够具体，使我们能够定位到距离发现地点0.25英里范围内的点——因此我们保留了这些案例。

与其他边境州的机构相比，德克萨斯州的机构提供的细节要少得多，例如遗体被发现前某人可能已死亡多久，或遗体腐烂程度进展如何。有些报告包含了这些信息，但许多没有。虽然尸检记录有时包含更多细节，但南德克萨斯州的大多数移民尸检由韦伯县法医办公室进行，该办公室对每份报告收费。鉴于我们分析的范围，这在成本上是不可行的。

《麻省理工科技评论》就如何将许多此类记录中提供的现场、尸体和死因描述转化为对某人可能死亡时间的粗略估计框架，咨询了亚利桑那州皮马县法医办公室主任格雷格·赫斯（Greg Hess）。（关于此过程的更多细节见下文。）

总之，我们在最终分析中包含了来自德克萨斯州记录请求的1,500多个案例。

直接获取亚利桑那州的记录

亚利桑那州皮马县法医办公室（PCOME）负责该州除尤马县以外的所有边境县的死亡调查工作（我们根据下文详述的内容，从“不再死亡”组织获取了尤马县的记录）。

该办公室确定其认为属于非法越境者的案件。它发布了一个关于移民死亡的数据门户，每月更新一次，并与人道边界组织（Humane Borders）共享数据，后者随后将其发布在地图和数据库中。我们包含了2015年至2026年4月的数据。

“人道边界”组织对每个案例的位置描述精度进行了备注。我们仅包含GPS坐标精确到300英尺以内的案例。自2012年左右以来，收集这些坐标已成为标准做法。记录还包括对个体死亡时间的估计，范围从不到一天到发现遗骸前至少六到八个月不等。

总体而言，我们在分析中包含了来自“人道边界”组织的1,700多个案例。

由“不再死亡”组织收集的数据

为了获取加利福尼亚州、新墨西哥州、亚利桑那州尤马县以及德克萨斯州埃尔帕索县和赫德佩斯县的死亡数据，我们求助于自2004年以来一直追踪移民死亡情况的非营利组织“不再死亡”。该组织发布了关于其记录请求和方法论的信息。

其数据库中的许多案例包括GPS坐标，有时附有说明位置仅为近似值的备注——例如，精确到半英里或一英里以内。我们仅包含那些位置已知在四分之一英里以内的案例。

2022年5月27日，在德克萨斯州伊格尔帕斯越过里奥格兰德河后，最终被边境巡逻队看守的移民（大多数带着孩子）沿着铁丝网路径行进。JOHN LAMPARSKI/NURPHOTO VIA AP

“不再死亡”组织的数据库包含（在可用时）关于每具遗骸被发现时的腐烂程度信息。与德克萨斯州的案例一样，《麻省理工科技评论》就如何将此信息转化为对某人可能死亡时间的粗略估计，咨询了PCOME的Greg Hess。

以下是我们分析中使用的“不再死亡”组织数据的来源：

在加利福尼亚州，“不再死亡”组织向圣地亚哥县法医办公室和帝国县验尸官申请记录。其关于帝国县的最新数据来自2025年12月，关于圣地亚哥县的最新数据来自2025年10月。

在亚利桑那州尤马县，“不再死亡”组织向尤马县法医办公室申请记录。最新数据来自2025年9月。

在新墨西哥州，该组织向州的医疗调查员办公室申请数据。与大多数州不同，新墨西哥州拥有全州范围内的法医体系，这使得“不再死亡”组织能够获得全州范围的移民死亡数据。最新数据来自2025年7月。

在德克萨斯州赫德佩斯县，“不再死亡”组织向第1区和第2区的治安法官申请记录。最新数据来自2023年12月。

在德克萨斯州埃尔帕索县，记录来自埃尔帕索县法医办公室。最新数据来自2025年9月。

总体而言，我们在分析中包含了来自“不再死亡”组织的近1,000个案例。

审查的案例总数

在考虑所有数据来源并排除那些因记录不够具体而无法确定遗骸发现地点的死亡案例后，我们总共分析了近4,000个案例。

其他说明

我们通常假设一个人在其遗骸被发现的地方死亡。这不一定正确：遗骸可能被其他人、流动的水或动物移动。但我们咨询的法医和研究人员表示，此类案例很少见。

我们排除了虚拟墙被认为不相关的案例。例如，我们删除了涉及在边境巡逻站内部死亡或在追逐过程中发生车祸的案例。

我们分析的死因反映了多种原因，乍看之下似乎属于不同类型的监控失效。例如，如果某人死在摄像头视野内，因脱水而缓慢死亡，那么相关人员就有更多的时间进行干预；而在某人迅速溺亡于河流或运河中的情况下，他们就没有那么多时间了。但我们纳入了所有这些死亡案例，因为在每一个案例中，虚拟墙本可以促使相关人员做出反应。

监控塔

将一座塔纳入我们的分析需要知道三件事：其位置、其类型（以便我们判断其设计观测距离），以及其安装时间。

位置

电子前哨基金会（EFF）自2023年以来一直在追踪和绘制美国海关与边境保护局（CBP）监控塔的地图，利用实地报道、卫星图像以及通过公共记录请求获得的政府文件。其统计数字存在低估；政府记录显示目前部署了约800座塔，而EFF记录了约600座。因此，我们的分析遗漏了发生在EFF尚未编目的塔附近的死亡事件。

在整个项目期间，《MIT科技评论》与EFF的调查主管Dave Maass密切合作。我们的塔数据始于EFF于2026年4月发布的数据库，但该地图未包含已拆除的塔。我们就这些前塔的详细信息咨询了EFF，并将它们添加到我们的数据库中。我们通常使用EFF为各个塔分配的参考编号，但为了确保每座塔都有唯一的标识符，我们更改了其中一些编号。

位置由GPS坐标标识。我们通过分析卫星图像验证了每座塔的坐标。

塔的类型

我们的分析集中在三种主要类型的塔上。EFF绘制的某些塔不属于这些类别中的任何一种，因此我们将它们排除在外，因为很难获得关于其设计观测距离的信息。这包括安装在边境巡逻检查站或哨所的一些塔。

亚利桑那州科奇斯县科罗纳多峰上的一座集成固定塔（IFT）。知识共享许可协议

新墨西哥州桑兰公园附近的一座自主监控塔（AST）。CENGIZ YAR 为 MITTR 拍摄

为了了解主要塔类型的观测距离，我们咨询了科技公司的资料、EFF的研究成果，对我们自己的政府文件进行了审查，并采访了前边境巡逻队员和官员。这些来源描述的观测距离是一致的。但这些是广告估算值，而非合同保证：一些政府记录以安全为由，对特定地点塔的监控范围更具体的信息进行了删减。

塔的存在时间

要确定现在存在的塔在某人死亡时是否已经存在，不仅要知道它的位置，还要知道它是何时安装的。为了弄清楚这一点，我们使用了多种卫星图像来源。

EFF的Maass此前曾分析过一些塔，以确定它们首次出现的时间。《MIT科技评论》检查了这些塔的卫星图像以确认这些时间线，然后检查了所有剩余的塔。对于每座塔，我们记录了它首次出现的日期，以及如果它最终消失，则记录其最后存在的日期。我们花了数月时间仔细核对数百座塔在多种卫星图像来源中出现的日期，以确认没有矛盾。

某些类型的塔比其他的更容易确定；例如，Anduril公司的塔往往建在没有先前基础设施的地方，很容易看出一片空旷的沙漠如何被新塔及其标志性的太阳能电池板所取代。其他类型的塔，如IFT，通常建在现有结构上或附近。对于这些塔，我们更多地依赖EFF在分析图像方面的专业知识。

当图像不足以说明情况时，我们使用Google街景、政府文件或EFF收集的照片来验证塔的搭建时间。

一个限制在于，并非每天都有边境沿线塔楼的历史图像可用。尤其是对于较旧的塔楼或位于偏远地区的塔楼，拍摄间隔可能长达数月甚至一年。一座在五月可见、十二月再次出现的塔楼，理论上可能在中间几个月被拆除并重新安装。但大多数塔楼系统是永久性结构。而且多个Borde

Our 15-month investigation into death and surveillance along the US-Mexico border began with a simple question: Why did so many people die near government surveillance towers meant to help track and apprehend them?

This story is part of Dying on Camera , a collaboration between MIT Technology Review and Times of San Diego . Journalists in both newsrooms spent the past year examining the failures of border surveillance technology and uncovering the stories of the people who die in the borderlands .

To answer that question, we looked through thousands of pages of government documents, visited the border multiple times, and interviewed more than 45 people, including current and former White House advisors, presidential appointees, Border Patrol agents, medical examiners, sheriffs, humanitarian volunteers, and employees of tech companies.

The result of our investigation is the first comprehensive map and analysis of deaths near border surveillance towers. Here’s how we built it, what decisions we made along the way, and what the data can and can’t tell us.

Our data

The investigation relied on knowing where migrants have died and where and when US Customs and Border Protection towers were installed. We analyzed cases dating back to 2015, allowing us to cover different border policies, presidential administrations, and tower technologies.

Migrant deaths

The US-Mexico border has been called the world’s deadliest land border, and Border Patrol estimates that more than 10,000 people have died during crossings since 2000—a figure that’s widely considered an undercount. But the amount of information available publicly on where and when these people died, and who they were, varies widely. Some remains are never discovered, and for those that are, there’s no national protocol for how the records are handled.

We considered a case for further analysis if we could confirm three basic things: whether the person was believed to have been crossing the border, where the remains were found, and roughly when the person died.

We created our dataset by merging existing ones that had been compiled and shared by other organizations, including No More Deaths, Humane Borders, and the Electronic Frontier Foundation, with new records we obtained ourselves from more than a dozen agencies.

Public records requests in Texas

Texas was the biggest missing link in most existing databases of migrant deaths. Unlike Arizona, it has no initiative to share records online, and unlike New Mexico, it leaves individual counties to handle their own death investigations. Some records for those individual counties existed, compiled by a handful of dedicated researchers, but nothing was comprehensive or current.

We identified 17 counties in Texas that would be relevant to our investigation: Culberson, Jeff Davis, Presidio, Terrell, Val Verde, Kinney, Maverick, Dimmit, Webb, Zapata, Jim Hogg, Starr, Hidalgo, Cameron, Kenedy, Brooks, and Duval. There are other counties in which migrants have died, but they do not have areas covered by surveillance towers and were therefore excluded.

In most of these counties, locally elected administrative judges called justices of the peace collect the most comprehensive information on local deaths. But records requests submitted to these individual judges can stall for years (indeed, some of our requests to justices of the peace remain unfilled more than a year after we filed them). Reports from justices of the peace sometimes leave out the scene or location details we needed; some justices never even visit the place where a migrant died, instead formally declaring the person deceased over FaceTime with the first responders on scene.

The border wall between Sunland Park, New Mexico and Puerto de Anapra, Mexico. GETTY IMAGES

MIT Technology Review instead filed records requests to the sheriffs of these 17 counties beginning in July 2025. These agencies are often first on the scene when a death is discovered, and their reports can have more detailed information on where remains were found. But relying on sheriffs’ records means our analysis undercounts migrant deaths in Texas, as it doesn’t include any deaths handled by local or state police.

After we filed a request, it took periods of near daily calls to the offices to receive the records, if we received them at all. Some were provided with no charge. Other counties charged between $300 and $1,300 to fill our request. Counties warned that their records were incomplete, with an unknown number lost during a move, damaged, destroyed, or misplaced during transitions between sheriffs.

Those delays were compounded because most agencies do not record whether a person is believed to have been crossing the border when they died. That’s despite provisions in some counties that allow officers to track far more granular details about other situations; Zapata County reports have a checkbox to indicate whether jewels were stolen in a burglary, for example, while Cameron County reports have one for whether a burglar entered through a chimney. Without a way to readily identify migrant deaths, offices had to pull records by hand, making the process slower, more costly, and more prone to error.

We received usable records from 14 of these counties (records have yet to be received from Dimmit or Duval, and Maverick’s office charged a per-record fee that was cost prohibitive).

Agencies generally sent us police reports for each individual case, amounting to over 4,000 pages of records in total. Some were handwritten documents.

Except for the reports from Kenedy, Webb, and Hidalgo Counties, we pulled out the relevant information by hand. For those three counties, which sent large volumes of records, we used Anthropic’s Claude, accessed via API, to inspect each case report and pull out coordinates of the spots where remains were found; then we checked batches of those cases by hand to verify the AI’s accuracy. Agencies sent us records on a rolling basis from July 2025 to February 2026, and most did not specify the date through which their records were current.

We generally trusted that agencies sent us cases they believed involved migrant deaths, since they had the most information about each case. But some records clearly suggested otherwise (indicating, for example, that someone died at home), and we excluded those cases.

Several hundred cases were removed from our analysis because they didn’t include enough information for us to be certain where the remains were found. In fewer than 100 cases, coordinates were not listed but the description was specific enough for us to locate a point within 0.25 miles of where they were found—so we kept those in.

Compared with agencies in other states along the border, those in Texas provide far fewer details regarding how long ago someone may have died before remains were found or how far the decomposition of those remains had progressed. Some reports included this information, but many didn’t. While autopsy records sometimes have more details, many migrant autopsies in south Texas are done through the Webb County Medical Examiner, which charges a fee for each report. That was cost prohibitive given the scale of our analysis.

MIT Technology Review consulted with Greg Hess, director of Arizona’s Pima County Office of the Medical Examiner, on a framework for translating descriptions of the scenes, bodies, and causes of death available in many of these records into rough estimates for when a person may have died (more detail on this process is provided below).

In total, we included more than 1,500 cases from our Texas records requests in our final analysis.

Accessing Arizona records directly

The Pima County Office of the Medical Examiner (PCOME) in Arizona handles death investigations for all border counties in the state except Yuma (we sourced Yuma's records from the organization No More Deaths, as detailed below).

The office determines which cases it believes to be border crossers. It publishes a data portal for these migrant deaths that’s updated monthly and shares its data with the organization Humane Borders, which then publishes it in a map and database . We included the data from 2015 through April 2026.

Humane Borders notes for each case how precise the location description is. We included only cases with GPS coordinates precise to within 300 feet. Collecting these coordinates has been standard practice since around 2012. The records also include an estimate of when the individual died, ranging from less than a day to at least six to eight months before remains were found.

In total, we included more than 1,700 cases from Humane Borders in our analysis.

Data collected by No More Deaths

To obtain data on deaths in California, New Mexico, Arizona’s Yuma County, and El Paso and Hudspeth Counties in Texas, we turned to the nonprofit organization No More Deaths, which has tracked migrant deaths since 2004. It publishes information about its records requests and its methodology .

Many of the cases in its database include GPS coordinates, sometimes with notes that the location is only approximate—for example, accurate to within half a mile or one mile. We included only cases where the location was known to within a quarter-mile.

Migrants, most with children, follow a path along the concertina wire where ultimately they will placed under guard by Border Patrol after having crossed the Rio Grande on May 27, 2022 in Eagle Pass, Texas. JOHN LAMPARSKI/NURPHOTO VIA AP

No More Death’s database includes, when available, information on the level of decomposition in which each set of remains was found. As with cases in Texas, MIT Technology Review consulted with PCOME’s Greg Hess on a framework for translating this information into rough estimates for when a person may have died.

Here’s where the No More Deaths data used in our analysis comes from:

In California, No More Deaths requests records from the San Diego County medical examiner and the Imperial County coroner. Its latest data for Imperial County is from December 2025, and its latest for San Diego County is from October 2025.

In Yuma County, Arizona, No More Deaths requests records from the Yuma County medical examiner. The latest data is from September 2025.

In New Mexico, the organization requests data from the state’s Office of the Medical Investigator. Unlike most states, New Mexico has a statewide medical examiner, allowing No More Deaths to obtain migrant death data for the entire state. The latest data is from July 2025.

For Hudspeth County, Texas, No More Deaths requests records from justices of the peace in Districts 1 and 2. The latest data is from December 2023.

For El Paso County, Texas, records were from the El Paso County Office of the Medical Examiner. The latest data is from September 2025.

In total, we included nearly 1,000 cases from No More Deaths in our analysis.

Total cases reviewed

When accounting for all our data sources and excluding deaths without specific enough records to determine where remains were found, we analyzed a total of nearly 4,000 cases.

Other notes

We generally assume that a person died where their remains were found. That may not necessarily be true: Remains can be moved by other people, flowing water, or animals. But medical examiners and researchers we consulted said such cases are rare.

We excluded cases in which the virtual wall did not appear relevant. For example, we removed cases involving people who died inside Border Patrol stations or in car crashes during pursuits.

The deaths we analyzed reflect a variety of causes that may seem at first like very different sorts of surveillance failure. If someone slowly died of dehydration within view of a camera, for example, agents would have had far more time to intervene than they would have in a case where someone drowned quickly in a river or canal. But we included all these deaths because, in each one, the virtual wall could have prompted a response from agents.

Surveillance towers

Including a tower in our analysis required knowing three things: its location, its type (so that we could judge how far it is supposed to see), and the time it was installed.

Locations

The Electronic Frontier Foundation has been tracking and mapping CBP surveillance towers since 2023, using on-the-ground reporting, satellite imagery, and government documents obtained through public records requests. Its tally is an undercount; government records suggest that about 800 towers are currently deployed, while EFF has logged about 600. Our analysis therefore misses deaths that occurred near towers not yet catalogued by EFF.

MIT Technology Review worked closely with EFF’s director of investigations, Dave Maass, throughout this project. Our tower data began with the database published by EFF in April 2026, but that map did not include towers that have been removed. We consulted EFF for the details on these former towers and added them to our database. We generally use EFF’s reference numbers for individual towers, but we changed some to ensure that each tower has a unique identifier.

The locations are identified by GPS coordinates. We verified each tower’s coordinates by analyzing satellite imagery.

Tower types

Our analysis focused on towers of three main types. Certain towers mapped by EFF don’t fall into any of those categories, so we excluded them because it’s difficult to obtain information about how far they are supposed to be able to see. This includes some towers that are installed at Border Patrol checkpoints or stations.

An integrated fixed tower (IFT) on Coronado Peak, Cochise County, Arizona. CREATIVE COMMONS

An autonomous surveillance tower (AST) near Sunland Park, New Mexico. CENGIZ YAR FOR MITTR

To know how far the main tower types could see, we consulted materials from tech companies and EFF’s research, led our own review of government documents, and interviewed former Border Patrol agents and officials. The distances described are consistent across these sources. But they are advertised estimates, not contractual guarantees: Some government records redact more specific information about a tower’s surveillance range in particular locations, citing security concerns.

When towers were present

To know if a tower in place now was present when someone died, it’s essential to know not just where it’s located but also when it was put there. To figure this out, we used multiple sources of satellite imagery.

Maass, at EFF, had previously analyzed some of the towers to determine when they first appeared. MIT Technology Review checked satellite imagery for these towers to confirm these timelines, and then checked for all the remaining towers. For each tower, we logged the date that it first appeared and, if it eventually disappeared, the last date it was present. We spent months meticulously checking when hundreds of towers appeared in multiple sources of satellite imagery to confirm there were no contradictions.

This is easier for certain tower types than others; towers from Anduril, for example, tend to go up where there was no prior infrastructure, and it’s fairly easy to see how a patch of empty desert gave way to the new tower and its trademark solar panels. Other towers, like IFTs, were often built on or near existing structures. For these, we leaned more closely on EFF’s expertise in analyzing the imagery.

When imagery wasn’t sufficient, we used Google Street View, government documents, or photographs collected by EFF to verify when towers went up.

One limitation is that historical imagery of towers along the border is not available for every day in the past. Especially for older towers or those in remote locations, images may have been taken months or even a year apart. A tower visible in May and again in December could theoretically have been removed and reinstalled in the intervening months. But most tower systems are permanent structures. And multiple Borde