In the same year, he was ordained a deacon for the Archdiocese of Zagreb and began postgraduate studies and specialization in the liturgy at the Pontifical Atheneum of St. Anselm.

Šaško successfully defended a dissertation on 28 November 1997, with the thesis Dona, munera, sancta sacrifício - and omnibus ... facere digneris: dinamismo pneumatologici part Canone Romano.

[1] In 1996 Šaško came back to Croatia and started working as an assistant in the Department of the liturgy of the Zagreb Catholic Theological Faculty.

In April 2005 he was elected associate professor in the Department of the liturgy of Zagreb Catholic Theological Faculty.

During three pastoral visits of Pope John Paul II to Croatia, he was one of those responsible for the preparation of liturgical celebrations.