Five inmates defend Amanda Knox during appeal

In Perugia, Italy, five witnesses are about to speak out in defense of Amanda Knox, the American who is in prison for killing her roommate in 2007. However, some are now questioning the witnesses' reliability.

CBS News Correspondent Charlie D'Agata reported there's plenty of courtroom drama as five serving inmates are coming forward to provide crucial inside information about the case.

But, D'Agata reported, prosecutors are doing everything they can to say these witnesses are hardened criminals who can't be trusted.

D'Agata reported on "The Early Show on Saturday Morning" that Amanda Knox looked composed and was dressed conservatively as she made the familiar journey into the Italian courtroom from the prison cell that's been her home for the past three-and-a-half years.

The new witnesses say she and former boyfriend Raffaele Sollecito are innocent of the murder of British student Meredith Kercher. A third man, Rudy Guede, has also been convicted of the murder.

The first witness to take the stand was convicted child killer Mario Alessi, a fellow inmate who said Rudy Guede told him that his friend killed Kercher.

Chris Mellas, Amanda Knox's stepfather, told CBS News, "We're hoping more truth comes out that these stories about Rudy and him speaking while in prison to the fact that Amanda had nothing to do with this, that it's proven in court."

But that's just one version, D'Agata reported. A second witness - convicted mobster Luciano Aviello - insists his bother murdered Kercher during a botched break-in.

Pictures: Amanda Knox: Case timeline
Pictures: Verdict in Italy

Today's testimonies are the latest twist in Knox's lengthy and ongoing appeal process. The 24-year-old Seattle student and her former boyfriend were convicted 18 months ago for the fatal stabbing of 21-year-old Kercher in the bedroom of the house they shared in the Italian mountain village of Perugia. She's serving a 26-year jail sentence, but in recent months, there have been growing doubts over the strength of her conviction.

A final decision in Knox's appeal is expected in the fall, but key to the case is the strength of the DNA. Lawyers say in terms of the murder weapon there was so little of Knox's DNA on it, it should never have been used as evidence in the first place.

Amanda Knox's parents, Edda Mellas and Kurt Knox, appeared on "The Early Show" with more on the case.

Kurt Knox said the new witnesses aren't that important to his daughter's case.

"It's more wrapped around, really, the DNA evidence that's going to be brought to the trial on the 30th of June," he said. "But you know, it's interesting that these inmates are coming forward at the risk of additional jail time, if they're, you know, slandering somebody per se, so that's kind of key."

"Early Show" co-anchor Rebecca Jarvis asked Kurt Knox about what he expects from the independent review of the DNA evidence involved in the case.

He replied, "My belief is that the accuracy of the first DNA set of tests that were done by the forensic police are going to come back as not being reliable by these independent experts and that's what we're really looking forward to."

Edda Mellas said lawyers are making progress in her daughter's case "little by little."

"They've been chipping away," Mellas said. "But I mean we really felt like in the first trial, even in the first trial, that there was no evidence, you know, that was brought forth to convict her. So you know, that surprised us, that they just don't give up, they keep going at it, because they believe in her and they know she's innocent."

Jarvis pointed out there have been reports that the Italian president himself is following his daughter's case.

Kurt Knox said, "It puts another eye on this particular case, and the fact it's so high-profile and so, you know, really wrong, and you know, having somebody keep an eye on it, I think, is just that much more beneficial to the result."

Mellas added, "It's not just the president. There have been lawmakers or you know, legislators in Italy who have all come out and said, 'Something's not right there. This needs to be looked at.' The president said, 'Yes' he's watching, it can only help."

As for Knox herself, her mother said she's doing everything she needs to survive behind bars.

"We tell her to stay strong," she said. "She gets huge messages of support from all over the world and she's really grateful for all of those, as are we, and we believe the truth will come out and that she'll be freed."