A decree adopted overnight Sunday now requires that any release be reviewed every two weeks to ensure that it was fully justified and remains so.
Some 376 mafiosi and drug dealers have been moved from jails to house arrest since March and judges were examining release requests from 456 others, the Repubblica daily reported on Thursday.
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Those freed include notorious 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.
The releases followed widespread riots in prisons in March by inmates fearful of catching the virus, which has killed some 30,000 people in Italy but there was much public unease given the seriousness of some of their crimes, prompting the government to backtrack.
“No one can think they can take advantage of the health emergency caused by the coronavirus to get out of prison,” Justice Minister Alfonso Bonafede was quoted as saying by the AGI news agency on Sunday.
“There is a new rule now which is going to put things straight,” Bonafede said.