After talking about Cardinal Stepinac, I found this blog/story on him. Cardinal William Joseph Levada held a mass for the 50th anniversary for when Cardinal Stepinac became a martyr. The ceremony took place in Rome in the Church of St. Girolamo.
The mass talked about the great things Stepinac had done and how he exemplify what a good person should be. Here's a quote...
"he lived what they stand for… sacrificing his own life for the truth and the unity of the Church in Croatia with the Successor of Peter.”
I'm not sure if a celebration took place in Zagreb. Since Stepinac is a national hero, there was probably a mass in Zagreb as well.