ROME, May 24 — The early release from prison this week of a mobster convicted of murder has touched off a furious debate in Italy about policies that reward even the worst killers if they provide information that helps put other members of the Mafia behind bars.

The mobster, Enzo Brusca, earned a ticket home this week, seven years after he went to prison for crimes that included the killing of the young son of another informer. He kidnapped the boy, who was 11 at the time, and held him captive for some time before strangling him and dissolving his body in acid.

Mr. Brusca, whose prison sentence was commuted to house arrest, is one of more than 1,100 criminal informers — called pentiti — who are collaborating with Italian law enforcement officials, the Interior Ministry says, and they have become the favorite weapons Italian judges use against criminal organizations.

The law providing for abbreviated sentences in return for information leading to significant arrests was passed a decade ago. Since then, Italians have come to view the practice as a necessary evil to root out the deeply entrenched Italian Mafia.

Still, the release of Mr. Brusca, who was serving a 30-year prison term, has struck a nerve. He is suspected of killing at least eight people, but it is the death of the informer's young son that bothers Italians.

Mr. Brusca's older brother, Giovanni Brusca, is serving a life sentence for his role in the car-bomb killings in 1992 of Italy's leading anti-Mafia judges, Giovanni Falcone and Paolo Borsellino. The killings enraged the nation, forcing a crackdown that resulted in the arrests of dozens of Mafia bosses.

In the uproar following Mr. Brusca's release, politicians have questioned the tribunal's wisdom. Even the Vatican, which usually stays out of Italy's more sordid affairs, published an editorial about the case on Wednesday in its daily newspaper, L'Osservatore Romano.

The justice minister, Roberto Castelli, has demanded an investigation. "These things bewilder opinion and undermine people's trust in justice," he said. "We are checking to see if everything has been done according to the law."

But some critics say the law is the problem. They contend that judges have too much discretion in reducing the sentences of informers. Some lawmakers are considering taking advantage of the momentum produced by Mr. Brusca's release to revise the legislation. They want to increase the mandatory amount of time a convicted killer must serve, regardless of whether he helps bring other mobsters to justice.

Paolo Cento, vice president of Parliament's justice commission, wants to impose a 15-year mandatory sentence for the gravest crimes. But Parliament had already toughened the law, in 2001, limiting the window for providing information and requiring informers to serve at least 10 years of a life sentence. Government officials said they doubted that the law would be re-evaluated now.

"Certainly this has hit the public opinion hard," said Alfredo Mantovano, an official responsible for the protection of the informers. "Emotions are high, but they will pass."

The main flaw in the system, Mr. Mantovano suggested, is that magistrates use the informers as a crutch to avoid more labor-intensive and costly investigations, but "one cannot do without them," he said.

"It is a balance of seeing if the costs exceed the advantages," Mr. Mantovano said. "We have seen great advantages, so we shouldn't be scandalized every time we need to pay the costs."