Bishop San Casimiro studied humanities in Lodosa (1952-1956) and in Fuenterrabia (1956-1960). He received the habit of the Augustinian Recollects in Monteagudo and, on the 6th of September of 1961 he made profession of vows. After four years of theological studies, he was ordained to the priesthood by Bishop Francisco Javier Ochoa on the 3rd of October of 1965.
In July of 1966, he was destined to Mexico but, due to bureaucratic obstacles was unable to obtain a permanent visa. On the 6th of October he arrived in Alajuela which would become the field of his labors for the next several years. He went to the United States in order to organize the establishment of the province in Texas (1969-1973) and between 1991-1994, he was the superior of the Augustinian Recollect community of Veracruz, Mexico.
During the 23 years of his priestly apostolate, he served mostly in Alajuela between the parishes of El Carmen (1973-1982 and 1994-1995) and San Antonio de Belen (1982-1991). He collaborated with the Cursillos de Cristiandad, the Charismatic Renewal, the Christian Family Movement, Youth Encounters, and other apostolic movements. From 1979 to 1985 and from 1994-1995, he was superior of the provincial delegation in Costa Rica and served as a member of the Priests Council of the Diocese of Alajuela.
In July of 1995, the Holy See named him the first bishop of Ciudad Quesada, a new diocese erected at the same date, October 7, 1995. The new bishop was ordained in a ceremony held in the football stadium of the city. Bsihop Giacinto Berlocco, papal nuncio was the ordaining prelate.
Bishop San Casimiro has served as treasurer of the Episcopal Conference of Costa Rica and president of the Commission for the Social Pastoral. In the Conference of Bishops of Latin America (CELAM) he became responsible for the Section in charge of dialogue with Non-Believers. He has also been secretary general of SEDAC (Episcopal Secretariat for Central America.
On the 3rd of July, His Holiness Benedict XVI named him Bishop of Alajuela. He took position of the diocese on October 12, the feast of Our Lady of Pilar.
The Diocese of Alajuela has an extension of 2, 381 square kilometers and a population of 662,520 inhabitants. The territory is divided into 31 parishes. There are 83 resident priests, 18 priest religious, 24 seminarians, 23 religious brothers and 60 female religious.