The incidents happened on 22 May when explosive devices blasted in front of the municipal headquarters of the eastern Croatian municipalities of Trpinja and Borovo.
According to Buconjic, the police have carried out a number of operational measures and although there is scarcity of traces and evidence, the circle of suspects has been tightened and the Interior Ministry, in cooperation with the Office of the State Prosecutor, is expecting the issuance of indictments.
About 25 persons have been investigated, a dozen of them have taken a polygraph test, and over ten houses and flats have been searched, Buconjic told MPs.
He added that an extensive probe had been launched into the murder of the Croatian citizen of Serb descent in the village of Karin in the Zadar hinterland.
In addition, the Counter-Intelligence Agency (POA) is engaged in this investigation, some 380 persons have been questioned, about ten of them passed polygraph tests, and DNA analyses have been carried out.
The police are about to finish this investigation, Buconjic said.