Allegedly it has been found that some priest of the Russian orthodox church in ukraine were working directly for the FSB. They helped gather information prior to the invasion, separating people into groups depending on likelyhood of collaboration. This information was used to make lists of unwanted individuals, slated for execution when the russians had taken over (which was supposed to happen 3 days after the invasion started.)

These are catholic priests that take confessions and are generally in a favorable position to extract information.