Italians were outraged Tuesday after a notorious mob boss was released from prison, where he served 25 years for a string of grim crimes, including assassinating a famous prosecutor and dissolving a boy's body in acid.

Giovanni Brusca, 64, was released Monday from Rome's Rebibbia prison after serving a 25-year sentence, during which he became a state's witness. He will now serve four years of probation.

"Brusca freed -- the cruellest boss," wrote La Repubblica daily.

But while some politicians and relatives of his victims denounced his release, others defended it given his cooperation with the authorities.

Brusca was a key figure within the Cosa Nostra, the Sicilian mafia group.

Falcone (2nd from the left) was killed with his wife and three bodyguards when a massive bomb exploded under his motorcade as it drove along a highway outside Palermo, Sicily
Falcone (2nd from the left) was killed with his wife and three bodyguards when a massive bomb exploded under his motorcade as it drove along a highway outside Palermo, Sicily AFP / GERARD FOUET

In 1992, he detonated the bomb that killed Giovanni Falcone, Italy's legendary prosecuting magistrate who dedicated his career to overthrowing the mafia.

Falcone's wife and three bodyguards were also killed in the attack after their car drove over a section of highway outside Palermo packed with 400 kilos (882 pounds) of explosives, detonated by Brusca nearby.

The wife of one of the bodyguards killed, Tina Montinaro, told Repubblica she was "indignant" at Brusca's release.

"The state is against us -- after 29 years we still don't know the truth about the massacre and Giovanni Brusca, the man who destroyed my family, is free," Montinaro said.

Falcone's sister, Maria, told the paper she was distressed by the news. But she added: "It's the law, a law moreover wanted by my brother and that should be respected."

Italian Judge Giovanni Falcone (2nd-L) arrives 21 October 1986 in Marseille to meet his French counterparts in charge to investigate the Mafia "Pizza Connection" criminal plot. Falcone, who won a reputation as being the Mafia's enemy number one, was kille
Italian Judge Giovanni Falcone (2nd-L) arrives 21 October 1986 in Marseille to meet his French counterparts in charge to investigate the Mafia "Pizza Connection" criminal plot. Falcone, who won a reputation as being the Mafia's enemy number one, was killed 23 May 1992 by a half-tone bomb which exploded under his motorcade as it drove along a highway outside Palermo, Sicily. AFP / GERARD FOUET

Brusca, who went by the nickname 'the Pig', was one of the most loyal operators of the head of Cosa Nostra, Salvatore "Toto" Riina.

Arrested in 1996, he decided to cooperate with the authorities, admitting to hundreds of murders, Italian news media reported.

One of the most grisly was the killing of 12-year-old Giuseppe Di Matteo, the son of a mafia turncoat, who was kidnapped in 1993 in retaliation for his father having collaborated with authorities.

A memorial marks the site of the murders at the site of the motorway
A memorial marks the site of the murders at the site of the motorway AFP / MARCELLO PATERNOSTRO

After being held in a house for over two years in squalid conditions, the boy was strangled and his body thrown into acid in what police have called "one of the most heinous crimes in the history of the Cosa Nostra".

"The law cannot be the same for these people," the boy's father Santino told the Corriere della Sera newspaper. "Brusca does not deserve anything."

"These people are not human," he added, recalling how Brusca "as well as my son, also killed a 23-year-old pregnant woman" who had nothing to do with the mafia, "after torturing her boyfriend".

He hoped he would never meet him in the street, he added. "I don't know what might happen."

Di Matteo himself still lives in a secret location for fear of mafia retribution.

There were protests, too, from both sides of Italy's political divide.

The leader of the centre-left Democratic Party, Enrico Letta, described the news as a "punch in the stomach that leaves one speechless".

Far-right leader Matteo Salvini called Brusca a "wild beast" who "cannot get out of prison".

But Pietro Grasso, a leftist politician and former Senate president who was once on the killer's hit-list, saw "no scandal".

Grasso served as a magistrate and was Italy's chief anti-mafia prosecutor before switching to politics in 2013.

He said he had little sympathy for Brusca, especially since the assassin and his aides had plotted to kill him and kidnap his son.

But he insisted that it was right to offer jail term reductions to mobsters who turn state informants.

"The indignation of many politicians who understand very little about the penal code and the fight against the mafia scares me," he wrote on Facebook.

"We need heavy jail term reductions for those who help the state, and the prospect of life imprisonment, with no reductions, for those who do not cooperate," Grasso said.