The years 1878-9 saw archaeological excavations held in Santiago Cathedral in order to attempt to unearth the remains of the primitive burial presumably concealed in the 16th century. The appearance of an ossuary in the cathedral apse prompted the carrying out of anatomical, chemical, archaeological, and historical studies to analyze the remains found. Upon completion of the process, Cardinal Payá sent affirmation of the discovery to Rome to request confirmation, which was received in 1884 with the Deus Omnipotens Papal Bull issued by Pope Leo XIII. The study on the evolution of the excavations, led by canons López Ferreiro and Labín, the investigations carried out and the development of the process in Rome is analyzed on the basis of the original documentation sent to the Sacred Congregation of Rites and preserved in the Vatican Secret Archives.