Colonel Boro Ivanovic, Lieutenant Colonel Dusan Loncar, Captain First Class Budimir Popadic, Captain Ilija Dekic and Captain Milomir Milosavljevic are suspected of ordering and leading artillery attacks on civilian targets in and around Osijek from June 1991 to May 1992.
The attacks left 87 civilians killed and 156 wounded, as well as extensive property damage.
The investigation order, issued on Wednesday, is based on a request filed by the County Prosecutor on 30 January.