De Chiara, 25, fell into a coma after his 12-round contest against Vincenzo Imparato on Saturday and doctors declared him dead less than 24 hours later.
Magistrates in the central town of Carrara, near where the fight took place, said they would study a video of the encounter and interview ringside spectators.
The referee ended the fight and De Chiara - the seventh Italian professional boxer to die from injuries sustained in the ring since the 1940s -made it back to his corner before collapsing. He died following two operations to remove blood that was putting pressure on his brain.
A devastated Imparato thought the fight should have been stopped in the 11th round. "I saw that [De Chiara] was short of breath and exhausted."
De Chiara's manager, Mario Loreni, said: "In the match he was always lucid. I asked `can you do it?' and he always said `yes'."
The death has led to calls in Italy for rules governing bouts and ringside medical care to be reviewed, while the sports daily Tuttosport wrote: "It's already doubtful whether on the threshold of the year 2000 two people should fight in a ring for money."
The state broadcaster RAI's decision to show recorded film of the entire fight on Saturday night after people already knew that De Chiara was in intensive care added to the controversy.
"The cynicism of man turned a drama into a macabre spectacle," L'Osservatore Romano commented.Reuse content