An investigation in Bosnia itself appears to have stalled.
Speaking to Italy's La Repubblica newspaper, Gavazzeni alleges that "many" took part in the practice, "at least a hundred" in all, with Italians paying "a lot of money" to do so, up to €100,000 (£88,000) in today's terms.
In 1992, late Russian nationalist writer and politician Eduard Limonov was filmed firing multiple rounds into Sarajevo from a heavy machine gun.
He was being given a tour of hillside positions by Bosnian Serb leader Radovan Karadzic, who was later convicted of genocide by an international tribunal in the Hague.
Limonov didn't pay for his war tourism, though. He was there as an admirer of Karadzic, telling the so-called Butcher of Bosnia: "We Russians should take example from you."
The fact Milan prosecutors had opened a case was first reported back in July when Il Giornale website wrote that the Italians would arrive in the mountains by minivan, paying huge bribes to pass checkpoints as they went, pretending to be on a humanitarian mission.
After a weekend shooting in the war zone, they would return home to their normal lives.
Gavazzeni described their actions as the "indifference of evil".
Prosecutors and police are said to have identified a list of witnesses as they try to establish who might have been involved.