The incident occurred on Tuesday afternoon as Hedl was passing by a cafe where Boras was sitting. Boras first verbally abused Hedl and then told him to go away or he would kill him.
In the Prosecutor's opinion, the threat has caused alarm and fear among reporters.
Under the Criminal Code, a person making a death threat against another faces a fine or a prison term of up to one year.
Hedl, who has been writing about war crimes committed in the Osijek area in the 1990s and the role of local power-broker Branimir Glavas in them, was accorded 24-hour police protection.
Boras became head of the youth organisation of the HDSSB, an association founded by Glavas, towards the end of 2005.