Recently, the U.S. state of Georgia executed Troy Davis. While Davis had been initially convicted of murder of a police officer, the majority of the eyewitnesses who implicated him recanted their testimonies, indicating that they had been coerced by police officers. Davis managed to secure an unusual re-hearing of his case. However, in the U.S., appeals (i.e. anything after the first trial) generally center on narrow, procedural grounds. At his re-hearing, Davis' lawyers had to prove that no reasonable juror would convict him, which was a nearly impossible bar to clear - in contrast, at a criminal trial, the prosecution is supposed to prove its case beyond a reasonable doubt to all the members of the jury. It is very difficult to challenge evidence at appeals trials in the U.S.
Several years ago, Amanda Knox and Rafaelle Sollecito were convicted in Italy of murder and sentenced to 26 years in prison. Since then, though, experts have argued that the investigation and the prosecution were flawed. In particular, forensic expert witnesses for the defense refuted the DNA evidence that Knox's DNA was on the murder weapon and that Sollecito's DNA was on the murder victim's clothing. It appears that the appeals trial did consider this new evidence - in contrast, Cameron Todd Willingham, who was most likely convicted of murder on the grounds of evidence of arson that was later disproven by experts, could not challenge the evidence at trial and had to resort to a direct appeal to the governor of Texas, who set up a commission (Gov. Perry later appears to have sabotaged this commission when they seemed to be leaning in favor of recommending a pardon. This commission was outside the regular judicial system, so they could not have overturned his conviction, whereas the Italian appeals court could, indeed, overturn Knox's and Sollecito's convictions.
Some U.S. commenters have cast aspersions on the Italian justice system. However, I would urge U.S. analysts of legal systems to note an interesting structural difference between Italy's system and the American one: flawed evidence can be more easily challenged in the former on appeal. Given the number of acquittals of people on death row from DNA evidence, the U.S. should look into that.
For the record, I am not absolutely against the death penalty in all circumstances - but I am absolutely against imprisoning or executing people who are not guilty as charged. The first line of defense does need to be ensuring that nobody is wrongfully imprisoned to begin with, but the above still holds. The Italian prosecutors said that Knox was lucky she was tried in Italy, as she would be given the death penalty in the U.S. - what's actually true is that had she been convicted in the U.S. on faulty evidence, she would most likely be screwed and be unable to reverse it on appeal.
PS - on the other hand, it also appears that the Italian appeals courts can increase a lower court's sentences, and that the prosecutors have requested that they sentence both Sollecito and Knox to life.
PPS - it appears that the appeals court exonerated both Sollecito and Knox. Our prayers should be with Meredith Kerchner, the murder victim, and her family.