Here's the exercise: imagine being a Croat in 1944.
You live in a tiny country which is only newly independent.
There are two enormous powers fighting to control the Continent.
Neither of them are attractive.
However, one offers to leave your country relatively intact, while the other promises to rip your society to shreds and incorporate it into its empire.
You've seen the Nazis give the defeated French some relative autonomy and home rule. You've seen the Communists literally slaughter and rape millions of Ukrainians - most of whom didn't even rebel!
So you're pretty sure that the Nazis represent a less pressing, longer-term problem, while the Communists will rape your wife and kill your children as soon as they get over your border.
That's the likely thought process of the normal, patriotic Croat in 1944.
If these men were Ustashe, they should have been imprisoned in Austria and tried for war crimes. If they were Croatian army regulars, they were probably innocent of anything other than daring to stand up to Stalin.