Legacy information systems age over time as a consequence of the uncontrolled maintenance and need to be modernized. Process mining allows the discovery of business processes embedded in legacy information systems, which is necessary to preserve the legacy business knowledge, and align them with the new, modernized information systems. There are two main approaches to address the mining of business processes from legacy information systems: (i) the static approach that only considers legacy source code's elements from a syntactical viewpoint; and (ii) the dynamic approach, which also considers information derived by system execution. Unfortunately, there is a lack of empirical evidence facilitating the selection of one of them. This paper provides a formal comparison of the static and dynamic approach through a case study. This study shows that the static approach provides better performance, while the dynamic approach discovers more accurate business processes.