There's an awful lot of Serbian-apologist type stuff floating around on FR presumably from Serbian-Americans....that is often of very dubious factual value. Be careful. Particularly when it tries to paint the Bosnians as a bunch of raving fundamentalist Muslims...there probably wasn't a less-religious Muslim community in the world than the Bosnians prior to the Bosnian Civil War. But, after it was going on a few years and the Serbs had managed to massacre whatever Bosnian Muslims they could get their hands on (Of course, all three sides in the conflict committed atrocities...the Serbs were the worst merely because they could be..they were the best armed and most powerful) various extremist Islamic factions did try to enter the region, recruit, etc, and they certainly were able to find a small number of radicalized adherents.
Note..I don't have a dog in that fight...I'm 1/2 In-America-for-400-years-English, and 1/2 Roman Catholic Slovak..not even near Yugoslavia, and just an interested observer.
Maybe he's just a Croat with mental problems. Let's hope.
Tito kept Yugoslavia under his boot and under control. Milosevic was a brutal communist who deserves to rot in prison. The Serbian people had to suffer under his tyranny.
OTOH, you're right about Croatia; it's not a predominantly Muslim nation.
That being said, the fact that this gentleman had a foreign passport definitely needs to be followed up. The dead murderer may have been using a false identity and/or passport. A Croatian passport would raise less eyebrows at INS than would someone with say a Bosnian, Yugoslavian or Macedonian passport. And it definitely would raise less eyebrows than an Afghani or Iraqi passport.