[2] Petkūnas returned to Lithuania and became a physician of bishop Jan Domanowski [pl] as well as the Calvinist supporter Mikołaj "the Black" Radziwiłł.
[4] The diocese did not have a permanent bishop for about four years and Petkūnas found it neglected and affected by the Protestant Reformation.
[6] He supported reconstruction of the Church of St. Francis and St. Bernard in Vilnius and bequeathed religious paintings from Holland, liturgical objects and robes to Varniai Cathedral.
In his last will, Petkūnas left 1,700 kopas of Lithuanian groschens to send twelve students to the Jesuit Academy in Vilnius.
[3] Petkūnas was ridiculed in In quendam antistitem, a Latin poem by Pedro Ruiz de Moros [pl], a Spaniard working in Vilnius, for neglecting his duties and spending his time hunting.
Valančius also quoted Albert Wijuk Kojałowicz who claimed that at the time of Petkūnas, the diocese was so neglected that it had just seven priests.