Introduction: Criminalistics is an auxiliary science of criminal law, which has been given different names and several concepts according to the schools that have been dedicated to its study, under this precept it can be said that criminalistics is an auxiliary science of criminal law that is responsible for the recognition, specification and evaluation of the evidence collected at the scene of the facts. Objectives: In this research, a critical legal analysis was carried out on the errors of the judicial assistants in the crime of robbery with death at the time of collecting the evidence at the scene of the event in Ecuador. Methodology: the research presents a qualitative approach, an exhaustive bibliographic review was carried out, as well as analytical-synthetic, inductive-deductive, historical-logical and dogmatic methods, in addition to bibliographic review techniques. Results: after the critical analysis, it was justified that, although it is true that criminalistics personnel are the auxiliaries of justice and through their work they help to discover the path to the truth of the events that occurred, however, in reality they make many errors that take their toll within a judicial process, even reaching the annulment of a test that can become of vital importance for the realization of the investigation. justice. Conclusions: It is necessary for criminalistics personnel to have their knowledge updated, with new techniques to carry out the collection of evidence at the scene of the facts, to adequately carry out the chain of custody procedures, starting with the collection of evidence, packaging, transport and analysis. General Area of Study: Law. Specific area of study: Procedural Law.