Italy's judicial system allows for two levels of appeals, and prosecutors can appeal acquittals.
The sentences and acquittals provoked howls of outrage both inside and outside the courtroom.
The new bill would abolish the prosecution's right to appeal against acquittals by the court of first instance.
The acquittals came after the judge dismissed the evidence of the two main prosecution witnesses, Robert and Ian Stewart.
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Because of time she served in prison before the appeals-level acquittals, Knox didn't have to serve time for the slander conviction.
In the second and final level of appeal, prosecutors are now seeking to overturn the acquittals, while defense attorneys say they should stand.
The Law Commission has also recommended that the prosecution should have the right to appeal against acquittals made on the direction of a judge.
In addition to the five acquittals, a sixth man, one of the village elders, had his death sentence commuted to life imprisonment last week.
After acquittals in high-profile trials such as that involving Robert Maxwell's empire, the case was held up as further evidence that jury trials were defective.
Defense attorneys said they were confident the acquittals would be upheld.
As a result of all this reality checking, trials are getting longer and more cases that might previously have resulted in quick convictions are now ending in acquittals.
The high court's ruling Tuesday overturned the appeals court acquittals.
Prosecutors are asking the high court to throw out the acquittals of American Knox and her Italian ex-boyfriend in the murder of 21-year-old British student Meredith Kercher, and order a new trial.
Most have owed less to clear-cut acquittals based on the evidence than to Italy's statute of limitations, or to recent changes in legislation apparently designed to benefit the prime minister as a defendant.
But the nightmare may not be over yet, as the pair are now expected to face what is in effect a retrial after prosecutors successfully argued that the acquittals had been "contradictory and illogical".
Yet the decision to go ahead with the arrest now is a sensitive one, after the controversial acquittals in recent months of a Kosovo Albanian and of a Bosniak who had been charged with murdering Serbs.
The number of acquittals is likely to disappoint survivors of the attacks and relatives of the victims, who said the trial had dredged up bad memories of the bombings that they could not now put to rest.
The acquittals were welcomed by observers.
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The decision by Italy's highest criminal appeals court to overturn the acquittals of American student Amanda Knox and her former Italian boyfriend, and order a new trial in the 2007 slaying of her British roommate, is once again raising concerns both at home and abroad about how justice works in Italy.
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