To be fair, the Bulgarians (and Macedonians) haven't done much killings since the two balkan wars before ww1. They tend to co-exist mostly peacefully with their neighbors, especially the last 15 years.

The serbians have been the ones trying to kill almost every other ethnicity around them. They are the bad guys of the region, yet they tend to claim victimhood the most (from NATO, to Croatians in WW2, to XXX ethnicity...).