The 376 mafiosi and drug dealers have been moved from overcrowded jails to house arrest since March and judges were examining release requests from 456 others, the La Repubblica newspaper said on Thursday.
Those allowed home include Cosa Nostra boss Francesco Bonura, 78, and Franco Cataldo, 85, who was part of a gang which murdered the teenage son of a turncoat in 1996 and dissolved his body in acid.
Officials had said inmates aged over 70 could leave jail if they suffered from health issues which made them vulnerable to Covid-19 – but judges were not instructed to differentiate between standard prisoners and mobsters.
The decision followed deadly riots in prisons across Italy in March lead by inmates fearful of catching the virus, which has since killed some 30,000 people in Italy.
The hundreds of mafia-linked criminals were put under house arrest, along with some 6,000 other convicts in Italy already serving their sentences at home after being handed a sentence of less than an 18 months.
A Carabinieri police officer stands guard outside the San Vittore prison in Milan during riots in March. Photo: AFP
Italy's anti-mafia prosecutor Federico Cafiero De Raho said on Thursday it was particularly odd to have let out those serving time under the country's harsh prison isolation regime, known as the 41-bis
The often-criticised regime isolates mobster bosses entirely to prevent them from running their clans from behind bars.
“If they are in isolation, it's obvious they cannot catch it, or be contagious,” he said.
De Raho said on Thursday that the release of these prisoners wasn't necessary.
“People got carried away by fears of contagion, when thermal scanners would have been enough,” he told Italian radio.
Critics also pointed out the virus has now been largely contained and Italy has now begun lifting its national lockdown.
Justice Minister Alfonso Bonafede said he was drawing up a decree to allow judges to review the release decisions now the pandemic has eased, and each new request would go through anti-mafia judges as well.