Police began investigating the death of an Italian football supporter on Thursday morning.
An Inter Milan fan died following a 60-person brawl with Napoli ultras in Milan on Wednesday evening, ahead of the two sides Serie A fixture at the San Siro Stadium.
The 35-year-old victim, who was hit by a van, was reportedly sent to hospital for emergency surgery before succumbing from his injuries.
Four others were stabbed in the fight by ultras armed with knives and hammers, according to local media.