Bulgarian Interior Ministry secretary-general Boyko Borissov confirmed the arrest but did not divulge the suspect's name or the circumstances of the arrest. He said DNA tests showed the arrested man was linked to a series of killings which shocked Bulgarians.
The wanted Croats are suspected of five murders, of which two were committed last week.
Borissov visited Zagreb yesterday and held talks with top Interior Ministry officials.
After the talks it was said the Croatian and Bulgarian police forces agreed to exchange data and cooperate in combating organised crime. Sources at the Croatian Interior Ministry declined to confirm or deny whether the main reason for Borissov's visit was a Bulgarian police investigation into the mob hits of which Croatian citizens are suspected.