In this article I present a paradigmatic case to exemplify how cross-examining sources constitutes one of the core pillars of our research work. I argue that a primary source, which can be easily regarded as a piece of evidence that is beyond accidental or intentional alterations, that can only convey veracity, and is, therefore, broadly speaking, authentic, must also be cross-examined. There is no such thing, or there should be no such thing as a primary source invested with an aura of sanctity, exempt from the need for verification. The critical examination of sources, that process of comparing and contrasting information, is to our profession what the microscope and reagents are to the natural sciences. Cross-examining pieces of evidence constitutes the crux of all research work, as a piece of evidence is, as a rule, an incomplete and imperfect piece in the puzzle. But no matter how incomplete and imperfect they may be, those fragments of evidence are all we have to recreate the past. Tracing the origins of a tiny detail, such as a handwritten note in a mostly typewritten archival document, can be the thread that gives us the answer to a series of questions. From now on, all meticulous research work will consist of pulling this thread so that it may lead us to new and better explanations. That tiny detail is what we have been waiting for in order to finally piece together the pattern. This article is made from the analysis of documents from the Guatemalan Army, documentary collections from the Historical Archive of the National Police, newspapers, declassified documents from the United States Government, and oral sources. 

在本文中，我提出了一个典型案例来举例说明交叉检验来源如何构成我们研究工作的核心支柱之一。我认为，主要来源很容易被视为超越偶然或故意更改的证据，只能传达真实性，因此从广义上讲是真实的，也必须进行交叉审查。不存在这样的东西，或者不应该存在这样的东西，即具有神圣光环的主要来源，无需验证。对来源的严格检查，即比较和对比信息的过程，对于我们的专业来说就像显微镜和试剂对于自然科学一样。交叉检验证据构成了所有研究工作的关键，因为证据通常是拼图中不完整且不完美的一块。但无论它们多么不完整和不完美，这些证据碎片都是我们重建过去所拥有的一切。追踪一个微小细节的起源，例如大部分打字的档案文档中的手写笔记，可以成为为我们提供一系列问题答案的线索。从现在开始，所有细致的研究工作都将围绕这条线索展开，以便它可以引导我们得到新的、更好的解释。这个微小的细节正是我们一直在等待的，以便最终拼凑出图案。本文是根据危地马拉军队的文件、国家警察历史档案馆的文献集、报纸、美国政府的解密文件和口头资料进行分析而成的。